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An acronym is a word or name formed as an abbreviation from the initial components in a phrase or a word, usually individual letters (as in NATO or laser) and sometimes syllables (as in Benelux).

There is no universal standardization of the various names for such abbreviations and of their orthographic styling. In English and most other languages, such abbreviations historically had limited use, but they became much more common in the 20th century. Acronyms are a type of word formation process, and they are viewed as a subtype of blending.

Nomenclature

Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, Rd for road or Dr for Doctor), an acronym is a word formed from the first letter or first few letters of each word in a phrase (such as sonar, created from sound navigation and ranging). Attestations for ' in German are known from 1921, and for acronym in English from 1940.
Paris Gazette, by Lion Feuchtwanger; translated (from Exil) by Willa and Edwin Muir, New York, Viking Press, 1940. Chapter 47, Beasts of Prey, pp.665–66:
His first glance at the _Paris German News_ told Wiesener that this new paper was nothing like the old _P.G._. "They can call it the _P.G.N._ if they like", he thought, "but that's the only difference. Pee-gee-enn; what's the word for words like that, made out of initials? My memory is beginning to fail me. Just the other day there was a technical expression I couldn't remember. I must be growing old. "_P.G._ or _P.G.N._, it's six of one and half a dozen of the other.... Pee-gee-enn. It's an acronym, that's what it is. That's what they call words made up of initials. So I remember it after all; that's at least something.
For "Akronym" used in 1921 or 1922, giving an example of "Agfa" film: Brockhaus Handbuch des Wissens in vier Bänden. Leipzig, F. A. Brockhaus, [1922–23, c1921-23] v. 1, p. 37.

Although the word acronym is often used to refer to any abbreviation formed from initial letters,Merriam-Webster, Inc. Merriam-Webster's Dictionary of English Usage, 1994. ISBN 0-87779-132-5. pp. 21–22:
acronyms  A number of commentators (as Copperud 1970, Janis 1984, Howard 1984) believe that acronyms can be differentiated from other abbreviations in being pronounceable as words. Dictionaries, however, do not make this distinction because writers in general do not:
"The powder metallurgy industry has officially adopted the acronym 'P/M Parts'"—Precision Metal Molding, January 1966."Users of the term acronym make no distinction between those pronounced as words ... and those pronounced as a series of characters" —Jean Praninskas, Trade Name Creation, 1968."It is not J.C.B.'s fault that its name, let alone its acronym, is not a household word among European scholars"—Times Literary Supp. 5 February 1970."... the confusion in the Pentagon about abbreviations and acronyms—words formed from the first letters of other words"—Bernard Weinraub, N.Y. Times, 11 December 1978. 

Pyles & Algeo 1970 divide acronyms into "initialisms", which consists of initial letters pronounced with the letter names, and "word acronyms", which are pronounced as words. Initialism, an older word than acronym, seems to be too little known to the general public to serve as the customary term standing in contrast with acronym in a narrow sense. many dictionaries and usage commentators define acronym to mean an abbreviation that is pronounced as a word, in contrast to an initialism (or alphabetism)an abbreviation formed from a string of initials (and possibly pronounced as individual letters). 
Some dictionaries include additional senses equating acronym with initialism.    The distinction, when made, hinges on whether the abbreviation is pronounced as a word or as a string of individual letters. Examples in reference works that make the distinction include NATO, scuba, and radar for acronyms - and FBI, CRT, and HTML for initialisms.
"acronym" Oxford English Dictionary. Ed. J.A. Simpson and E.S.C. Weiner. 2nd ed. Oxford: Clarendon Press, 1989. OED Online Oxford University Press. Accessed May 2, 2006.[http://www.merriam-webster.com/dictionary/crt CRT | Definition of CRT by Merriam-Webster] The rest of this article uses acronym for both types of abbreviation.

There is no rule on what to call abbreviations whose pronunciation involves the combination of letter names and words, such as JPEG and MS-DOS.  There is also some disagreement as to what to call abbreviations that some speakers pronounce as letters and others pronounce as a word. For example, the terms URL and IRA can be pronounced as individual letters: and, respectively; or as a single word: and, respectively.

The spelled-out form of an acronym or initialism (that is, what it stands for) is called its expansion.

Comparing a few examples of each type

*Pronounced as a word, containing only initial letters
**NATO: North Atlantic Treaty Organization
**Scuba: self-contained underwater breathing apparatus
**Laser: light amplification by stimulated emission of radiation
**GIF: Graphics Interchange Format
*Pronounced as a word, containing non-initial letters
**Amphetamine: alpha-methylphenethylamine
**Gestapo: ' ('secret state police')
**Interpol: International Criminal Police Organization
**Nabisco: National Biscuit Company
*Pronounced as a string of letters, containing non-initial letters
** PMN: polymorphonuclear leukocytes
** OCA: oculocutaneous albinism
** PCM: paracoccidioidomycosis
*Pronounced as a word, containing a mixture of initial and non-initial letters
**AIDS: acquired immunodeficiency syndrome
**Necco: New England Confectionery Company
**Radar: radio detection and ranging
*Pronounced as a word or as a string of letters, depending on speaker or context
**FAQ: ( or ef-ay-cue) frequently asked question
**IRA: When used for Individual Retirement Account, can be pronounced as letters (i-ar-a) or as a word.
**SAT(s): ( or ess-ay-tee) (previously)
***Scholastic Achievement (or Aptitude) Test(s) (US) (now claimed not to stand for anything ) or
***Standard Assessment Test(s) (UK)
**SQL: ( or ess-cue-el) Structured Query Language.
*Pronounced as a combination of spelling out and a word
**CD-ROM: (cee-dee-) Compact Disc read-only memory
**IUPAC: (i-u-) International Union of Pure and Applied Chemistry
**JPEG: (jay-) Joint Photographic Experts Group
**SFMOMA: (ess-ef-) San Francisco Museum of Modern Art

*Pronounced only as a string of letters
**BBC: British Broadcasting Corporation
**OEM: original equipment manufacturer
**USA: United States of America
**MEC: Mountain Equipment Co-Op  

*Pronounced as a string of letters, but with a shortcut
**AAA:
***(triple A) American Automobile Association; abdominal aortic aneurysm; anti-aircraft artillery; Asistencia, Asesoría y Administración
***(three As) Amateur Athletic Association
**IEEE: (I triple E) Institute of Electrical and Electronics Engineers
**NAACP: (N double A C P) National Association for the Advancement of Colored People
**NCAA: (N C double A or N C two A or N C A A) National Collegiate Athletic Association
*Shortcut incorporated into name
**3M: (three M) originally Minnesota Mining and Manufacturing Company
**(ISC)²: (ISC-squared) International Information Systems Security Certification Consortium 
**W3C: (W three C) World Wide Web Consortium
**C4ISTAR: (C four I star) Command, Control, Communications, Computers, Intelligence, Surveillance, Target Acquisition, and Reconnaissance 
*Multi-layered acronyms
**NAC Breda: (Dutch football club) NOAD ADVENDO Combinatie ("NOAD ADVENDO Combination"),formed by the 1912 merger of two clubs from Breda:
***NOAD(' "Never give up, always persevere")
***ADVENDO(' "Pleasant by entertainment and useful by relaxation")  
**GAIM (former name of Pidgin): GTK+ AOL Instant Messenger
**GIMP: GNU Image Manipulation Program
** VHDL: VHSIC hardware description language, where VHSIC stands for very-high-speed integrated circuit.
*Recursive acronyms, in which the abbreviation refers to itself
**GNU: GNU's not Unix!
** Wine: Wine is not an emulator (originally, Windows emulator)
**These may go through multiple layers before the self-reference is found:
***HURD: HIRD of Unix-replacing daemons, where "HIRD" stands for "HURD of interfaces representing depth"
*Pseudo-acronyms, which consist of a sequence of characters that, when pronounced as intended, invoke other, longer words with less typing 
**CQ: cee-cue for "seek you", a code used by radio operators
**IOU: i-o-u for "I owe you" (the true acronym would be IOY)
**K9: kay-nine for "canine", used to designate police units utilizing dogs
**Q8: cue-eight for "Kuwait"
*Abbreviations whose last abbreviated word is often redundantly included anyway
**ATM machine: automated teller machine (machine)
**HIV virus: human immunodeficiency virus (virus)
**LCD display: liquid crystal display (display)
**PIN number: personal identification number (number)

Historical and current use

Acronymy, like retronymy, is a linguistic process that has existed throughout history but for which there was little to no naming, conscious attention, or systematic analysis until relatively recent times. Like retronymy, it became much more common in the 20th century than it had formerly been.

Ancient examples of acronymy (regardless of whether there was metalanguage at the time to describe it) include the following:
* Acronyms were used in Rome before the Christian era. For example, the official name for the Roman Empire, and the Republic before it, was abbreviated as SPQR ('). Inscriptions dating from antiquity, both on stone and on coins, use a lot of abbreviations and acronyms to save room and work. For example, Roman first names, of which there was only a small set, were almost always abbreviated. Common terms were abbreviated too, such as writing just "F" for ', meaning "son of", a very common part of memorial inscriptions mentioning people. Grammatical markers were abbreviated or left out entirely if they could be inferred from the rest of the text.
* So-called ' were used in many Greek biblical manuscripts. The common words "God" (), "Jesus" (), "Christ" (), and some others, would be abbreviated by their first and last letters, marked with an overline. This was just one of many kinds of conventional scribal abbreviation, used to reduce the time-consuming workload of the scribe and save on valuable writing materials. The same convention is still commonly used in the inscriptions on religious icons and the stamps used to mark the eucharistic bread in eastern churches.
* The early Christians in Rome, most of whom were Greek rather than Latin speakers, used the image of a fish as a symbol for Jesus in part because of an acronym—fish in Greek is ' (), which was said to stand for  (': "Jesus Christ, God's Son, Savior"). This interpretation dates from the 2nd and 3rd centuries and is preserved in the catacombs of Rome. And for centuries, the Church has used the inscription INRI over the crucifix, which stands for the Latin ' ("Jesus the Nazarene, King of the Jews").
* The Hebrew language has a long history of formation of acronyms pronounced as words, stretching back many centuries. The Hebrew Bible ("Old Testament") is known as "Tanakh", an acronym composed from the Hebrew initial letters of its three major sections: Torah (five books of Moses), Nevi'im (prophets), and K'tuvim (writings). Many rabbinical figures from the Middle Ages onward are referred to in rabbinical literature by their pronounced acronyms, such as Rambam and Rashi from the initial letters of their full Hebrew names: Rabbi Moshe ben Maimon and Rabbi Shlomo Yitzkhaki.

During the mid- to late-19th century, an acronym-disseminating trend spread through the American and European business communities: abbreviating corporation names in places where space was limited for writing—such as on the sides of railroad cars (e.g., Richmond, Fredericksburg and Potomac Railroad → RF&P); on the sides of barrels and crates; and on ticker tape and in the small-print newspaper stock listings that got their data from it (e.g., American Telephone and Telegraph Company → AT&T). Some well-known commercial examples dating from the 1890s through 1920s include Nabisco (National Biscuit Company), Esso (from S.O., from Standard Oil), and Sunoco (Sun Oil Company).

Another driver for the adoption of acronyms was modern warfare with its many highly technical terms. While there is no recorded use of military acronyms in documents dating from the American Civil War (acronyms such as ANV for "Army of Northern Virginia" post-date the war itself), they had become somewhat common in World War I and were very much a part even of the vernacular language of the soldiers during World War II,  who themselves were referred to as G.I.s.

The widespread, frequent use of acronyms across the whole range of registers is a relatively new linguistic phenomenon in most languages, becoming increasingly evident since the mid-20th century. As literacy rates rose, and as advances in science and technology brought with them a constant stream of new (and sometimes more complex) terms and concepts, the practice of abbreviating terms became increasingly convenient. The Oxford English Dictionary (OED) records the first printed use of the word initialism as occurring in 1899, but it did not come into general use until 1965, well after acronym had become common.

By 1943, the term acronym had been used in English to recognize abbreviations (and contractions of phrases) that were pronounced as words.B. Davenport American Notes and Queries (February 1943) vol 2 page 167 "Your correspondent who asks about words made up of the initial letters or syllables of other words may be interested in knowing that I have seen such words called by the name acronym, which is useful and clear to anyone who knows a little Greek." (It was formed from the Greek words , ', "topmost, extreme" and , ', "name.") For example, the army offense of being absent without official leave was abbreviated to "A.W.O.L." in reports, but when pronounced as a word (awol), it became an acronym.  While initial letters are commonly used to form an acronym, the original definition was "a word made from the initial letters or syllables of other words",  for example UNIVAC from UNIVersal Automatic Computer. 

In English, acronyms pronounced as words may be a 20th-century phenomenon. Linguist David Wilton in Word Myths: Debunking Linguistic Urban Legends claims that "forming words from acronyms is a distinctly twentieth- (and now twenty-first-) century phenomenon. There is only one known pre-twentieth-century [English] word with an acronymic origin and it was in vogue for only a short time in 1886. The word is colinderies or colinda, an acronym for the Colonial and Indian Exposition held in London in that year."   However, although acronymic words seem not to have been employed in general vocabulary before the 20th century (as Wilton points out), the concept of their formation is treated as effortlessly understood (and evidently not novel) in a Poe story of the 1830s, "How to Write a Blackwood Article", which includes the contrived acronym P.R.E.T.T.Y.B.L.U.E.B.A.T.C.H.

Early examples in English

* The use of Latin and Neo-Latin terms in vernaculars has been pan-European and predates modern English. Some examples of acronyms in this class are:
**A.M. (from Latin ', "before noon") and P.M. (from Latin ', "after noon")
**A.D. (from Latin ', "in the year of our Lord"), whose complement in English, B.C. [Before Christ], is English-sourced
**O.K., a term of disputed origin, dating back at least to the early 19th century, now used around the world

Current use

Acronyms are used most often to abbreviate names of organizations and long or frequently referenced terms. The armed forces and government agencies frequently employ acronyms; some well-known examples from the United States are among the "alphabet agencies" (also jokingly referred to as "alphabet soup") created by Franklin D. Roosevelt (also of course known as FDR) under the New Deal. Business and industry also are prolific coiners of acronyms. The rapid advance of science and technology in recent centuries seems to be an underlying force driving the usage, as new inventions and concepts with multiword names create a demand for shorter, more manageable names. One representative example, from the U.S. Navy, is COMCRUDESPAC, which stands for commander, cruisers destroyers Pacific; it's also seen as "ComCruDesPac". "YABA-compatible" (where YABA stands for "yet another bloody acronym") is used to mean that a term's acronym can be pronounced but is not an offensive word, e.g., "When choosing a new name, be sure it is 'YABA-compatible'." 

Acronym use has been further popularized by text messaging on mobile phones with Short Message Systems (SMS). To fit messages into the 160-character SMS limit, acronyms such as "GF" (girlfriend), "LOL" (laughing out loud), and "DL" (download or down low) have become popular.  Some prescriptivists disdain texting acronyms and abbreviations as decreasing clarity, or as failure to use "pure" or "proper" English.  Others point out that language change has happened for thousands of years, and argue that it should be embraced as inevitable, or as innovation that adapts the language to changing circumstances. In this view, the modern practice is just as legitimate as those in "proper" English of the current generation of speakers, such as the abbreviation of corporation names in places with limited writing space (e.g., ticker tape, newspaper column inches).

Aids to learning the expansion without leaving a document

In formal writing for a broad audience, the expansion is typically given at the first occurrence of the acronym within a given text, for the benefit of those readers who do not know what it stands for. The capitalization of the original term is independent of it being acronymized, being lowercase for a common noun such as frequently asked questions (FAQ) but uppercase for a proper noun such as the United Nations (UN) (as explained at Case > Casing of expansions).

In addition to expansion at first use, some publications also have a key listing all acronyms used therein and what their expansions are. This is a convenience to readers for two reasons. The first is that if they are not reading the entire publication sequentially (which is a common mode of reading), then they may encounter an acronym without having seen its expansion. Having a key at the start or end of the publication obviates skimming over the text searching for an earlier use to find the expansion. (This is especially important in the print medium, where no search utility is available.) The second reason for the key feature is its pedagogical value in educational works such as textbooks. It gives students a way to review the meanings of the acronyms introduced in a chapter after they have done the line-by-line reading, and also a way to quiz themselves on the meanings (by covering up the expansion column and recalling the expansions from memory, then checking their answers by uncovering.) In addition, this feature enables readers possessing knowledge of the abbreviations not to have to encounter expansions (redundant to such readers).

Expansion at first use and the abbreviation-key feature are aids to the reader that originated in the print era, and they are equally useful in print and online. In addition, the online medium offers yet more aids, such as tooltips, hyperlinks, and rapid search via search engine technology.

Jargon

Acronyms often occur in jargon. An acronym may have different meanings in different areas of industry, writing, and scholarship. The general reason for this is convenience and succinctness for specialists, although it has led some to obfuscate the meaning either intentionally, to deter those without such domain-specific knowledge, or unintentionally, by creating an acronym that already existed.

The medical literature has been struggling to control the proliferation of acronyms as their use has evolved from aiding communication to hindering it. This has become such a problem that it is even evaluated at the level of medical academies such as the American Academy of Dermatology.
 

As mnemonics

Acronyms are often taught as mnemonic devices, for example in physics the colors of the visible spectrum are ROY G. BIV (red-orange-yellow-green-blue-indigo-violet). They are also used as mental checklists, for example in aviation: GUMPS, which is Gas-Undercarriage-Mixture-Propeller-Seatbelts. Other examples of mnemonic acronyms include CAN SLIM, and PAVPANIC.

Acronyms as legendary etymology

It is not uncommon for acronyms to be cited in a kind of false etymology, called a folk etymology, for a word. Such etymologies persist in popular culture but have no factual basis in historical linguistics, and are examples of language-related urban legends. For example, cop is commonly cited as being derived, it is presumed, from "constable on patrol,"  and posh from "port out, starboard home".  With some of these specious expansions, the "belief" that the etymology is acronymic has clearly been tongue-in-cheek among many citers, as with "gentlemen only, ladies forbidden" for golf, although many other (more credulous) people have uncritically taken it for fact.  Taboo words in particular commonly have such false etymologies: shit from "ship/store high in transit"  or "special high-intensity training" and fuck from "for unlawful carnal knowledge", or "fornication under consent/command of the king".

Orthographic styling

Punctuation

Showing the ellipsis of letters

In English, abbreviations have traditionally been written with a full stop/period/point in place of the deleted part to show the ellipsis of letters – although the colon and apostrophe have also had this role – and with a space after full stops (e.g. "A. D."). In the case of most acronyms, each letter is an abbreviation of a separate word and, in theory, should get its own termination mark. Such punctuation is diminishing with the belief that the presence of all-capital letters is sufficient to indicate that the word is an abbreviation. 

Ellipsis-is-understood style

Some influential style guides, such as that of the BBC, no longer require punctuation to show ellipsis; some even proscribe it. Larry Trask, American author of The Penguin Guide to Punctuation, states categorically that, in British English, "this tiresome and unnecessary practice is now obsolete".

Pronunciation-dependent style and periods

Nevertheless, some influential style guides, many of them American, still require periods in certain instances. For example, The New York Times' guide recommends following each segment with a period when the letters are pronounced individually, as in K.G.B., but not when pronounced as a word, as in NATO.
 The logic of this style is that the pronunciation is reflected graphically by the punctuation scheme.

Other conventions

When a multiple-letter abbreviation is formed from a single word, periods are in general not used, although they may be common in informal usage. TV, for example, may stand for a single word (television or transvestite, for instance), and is in general spelled without punctuation (except in the plural). Although PS stands for the single word postscript (or the Latin postscriptum), it is often spelled with periods (P.S.).

The slash ('/', or solidus) is sometimes used to separate the letters in a two-letter acronym, as in N/A (not applicable, not available), c/o (care of) and w/o (without).

Inconveniently long words used frequently in related contexts can be represented according to their letter count. For example, i18n abbreviates internationalization, a computer-science term for adapting software for worldwide use. The 18 represents the 18 letters that come between the first and the last in internationalization. Localization can be abbreviated l10n, multilingualization m17n, and accessibility a11y. In addition to the use of a specific number replacing that amount of letters, the more general "x" can be used to replace an unspecified number of letters. Examples include Crxn for crystallization and the series familiar to physicians for history, diagnosis, and treatment (hx, dx, tx).

Representing plurals and possessives

There is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, Kate Turabian, writing about style in academic writings,  allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" and "Ph.D.'s". The Modern Language Association  and American Psychological Association Publication Manual of the American Psychological Association (APA), 6th Edition 2010, subsection 4.29 prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas the New York Times style guide requires an apostrophe is necessary when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's"). 

Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, the C.D.'s' labels (the labels of the compact discs). This is yet another reason to use apostrophes only for possessives and not for plurals. In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is S, as in SOS's (although abbreviations ending with S can also take -es, e.g. SOSes), or when pluralizing an abbreviation that has periods. 

A particularly rich source of options arises when the plural of an acronym would normally be indicated in a word other than the final word if spelled out in full. A classic example is Member of Parliament, which in plural is Members of Parliament. It is possible then to abbreviate this as M's P.  (or similar), as used by former Australian Prime Minister Ben Chifley.[http://nla.gov.au/nla.news-page5605107 02 Dec 1948 – Townsville Daily Bulletin – p1][http://nla.gov.au/nla.news-article27755397 14 Oct 1948 – PRIME MINISTER ASSERTS M's.P. HAVE NO IMMUNITY F][http://www.electricscotland.com/history/australia/melbourne11.htm The Royal Caledonian Society of Melbourne] This usage is less common than forms with s at the end, such as MPs, and may appear dated or pedantic. In common usage, therefore, weapons of mass destruction becomes WMDs, prisoners of war becomes POWs, and runs batted in becomes RBIs. 

The argument that acronyms should have no different plural form (for example, "If D can stand for disc, it can also stand for discs") is in general disregarded because of the practicality in distinguishing singulars and plurals. This is not the case, however, when the abbreviation is understood to describe a plural noun already: For example, U.S. is short for United States, but not United State. In this case, the options for making a possessive form of an abbreviation that is already in its plural form without a final s may seem awkward: for example, U.S., U.S.'s, etc. In such instances, possessive abbreviations are often foregone in favor of simple attributive usage (for example, the U.S. economy) or expanding the abbreviation to its full form and then making the possessive (for example, the United States' economy). On the other hand, in speech, the pronunciation United States's sometimes is used.

Abbreviations that come from single, rather than multiple, words—such as TV (television)—are usually pluralized without apostrophes (two TVs); most writers feel that the apostrophe should be reserved for the possessive (the TV's antenna).

 In some languages, the convention of doubling the letters in the acronym is used to indicate plural words: for example, the Spanish ', for ' ('United States'). This old convention is still followed for a limited number of English abbreviations, such as SS. for "Saints", pp. for the Latin plural of "pages", ', or MSS for "manuscripts".

Case

All-caps style

The most common capitalization scheme seen with acronyms is all-uppercase (all-caps), except for those few that have linguistically taken on an identity as regular words, with the acronymous etymology of the words fading into the background of common knowledge, such as has occurred with the words scuba, laser, and radar—these are known as anacronyms. 

Small-caps variant

Small caps are sometimes used to make the run of capital letters seem less jarring to the reader. For example, the style of some American publications, including the Atlantic Monthly and USA Today, is to use small caps for acronyms longer than three letters; thus "U.S." and "FDR" in normal caps, but "" in small caps. The acronyms "AD" and "BC" are often smallcapped as well, as in: "From ".

Mixed-case variant

Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, pre-WWII politics, post-NATO world, DNAase. In some cases a derived acronym may also be expressed in mixed case. For example, messenger RNA and transfer RNA become mRNA and tRNA.

Pronunciation-dependent style and case

Some publications choose to capitalize only the first letter of acronyms, reserving all-caps styling for initialisms. Thus the pronounced acronyms "Nato" and "Aids" are mixed-case, but the initialisms "USA" and "FBI" are capital-only. For example, this is the style used in The Guardian,  and BBC News typically edits to this style (though its official style guide, dating from 2003, still recommends all-caps ). The logic of this style is that the pronunciation is reflected graphically by the capitalization scheme.

Some style manuals also base the letters' case on their number. The New York Times, for example, keeps NATO in all capitals (while several guides in the British press may render it Nato), but uses lower case in UNICEF (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals").

Numerals and constituent words

While abbreviations typically exclude the initials of short function words (such as "and", "or", "of", or "to"), this is not always the case. (A similar set of words is sometimes left as lowercase in headers and publication titles.) Sometimes function words are included to make a pronounceable acronym, such as CORE (Congress of Racial Equality). Sometimes the letters representing these words are written in lower case, such as in the cases of TfL (Transport for London) and LotR (Lord of the Rings); this usually occurs when the acronym represents a multi-word proper noun.

Numbers (both cardinal and ordinal) in names are often represented by digits rather than initial letters: as in 4GL (Fourth generation language) or G77 (Group of 77). Large numbers may use metric prefixes, as with Y2K for "Year 2000" (sometimes written Y2k, because the SI symbol for 1000 is k—not K, which stands for kelvin). Exceptions using initials for numbers include TLA (three-letter acronym/abbreviation) and GoF (Gang of Four). Abbreviations using numbers for other purposes include repetitions, such as W3C ("World Wide Web Consortium") and T3 (Trends, Tips & Tools for Everyday Living); pronunciation, such as B2B ("business to business"); and numeronyms, such as i18n ("internationalization"; 18 represents the 18 letters between the initial i and the final n).

Casing of expansions

Although many authors of expository writing show a predisposition to capitalizing the initials of the expansion for pedagogical emphasis (trying to thrust the reader's attention toward where the letters are coming from), this sometimes conflicts with the convention of English orthography, which reserves capitals in the middle of sentences for proper nouns. Enforcing the general convention, most professional editors case-fold such expansions to their standard orthography when editing manuscripts for publication. The justification is that (1) readers are smart enough to figure out where the letters came from, even without their being capitalized for emphasis, and that (2) common nouns do not take capital initials in standard English orthography.  Such house styles also usually disfavor bold or italic font for the initial letters. For example,
"the onset of Congestive Heart Failure (CHF)" or "the onset of congestive heart failure (CHF)" if found in an unpublished manuscript would be rewritten as "the onset of congestive heart failure (CHF)" in the final published article when following the AMA Manual of Style. 

Changes to (or word play on) the expanded meaning

Pseudo-acronyms
 
Some apparent acronyms or other abbreviations do not stand for anything and cannot be expanded to some meaning. Such pseudo-acronyms frequently develop as "orphan initialisms"; an existing acronym is redefined as a non-acronymous name, severing its link to its previous meaning.[http://itre.cis.upenn.edu/~myl/languagelog/archives/003555.html Language Log: Orphan initialisms][http://grammar.about.com/b/2010/06/02/what-does-bp-stand-for.htm What Does "BP" Stand For?]  For example, the letters of the SAT, a US college entrance test originally dubbed "Scholastic Aptitude Test", no longer officially stand for anything.  

This is common with companies that want to retain brand recognition while moving away from an outdated image: American Telephone and Telegraph became AT&T, Kentucky Fried Chicken became KFC to de-emphasize the role of frying in the preparation of its signature dishes,  and British Petroleum became BP.  Russia Today has rebranded itself as RT.

Pseudo-acronyms may have advantages in international markets: for example, some national affiliates of International Business Machines are legally incorporated as "IBM" (for example, "IBM Canada") to avoid translating the full name into local languages. Likewise, "UBS" is the name of the merged Union Bank of Switzerland and Swiss Bank Corporation,  and  "HSBC" has replaced "The Hong Kong and Shanghai Banking Corporation."

The UK defence contractor BAE Systems was formed when British Aerospace (BAe) merged with Marconi Electronic Systems (MES). According to the company's branding policy, the BAE part of the name is said to "not stand for anything" and the company insist that "we are always BAE Systems, never BAE or BAES".

Redundant acronyms and RAS syndrome

Rebranding can lead to redundant acronym syndrome, as when Trustee Savings Bank became TSB Bank, or when Railway Express Agency became REA Express. A few high-tech companies have taken the redundant acronym to the extreme: for example, ISM Information Systems Management Corp. and SHL Systemhouse Ltd. An example in entertainment is the television shows CSI: Crime Scene Investigation and Navy: NCIS (Navy was dropped in the second season), where the redundancy was likely designed to educate new viewers as to what the initials stood for. The same reasoning was in evidence when the Royal Bank of Canada's Canadian operations rebranded to RBC Royal Bank, or when Bank of Montreal rebranded their retail banking subsidiary BMO Bank of Montreal.

Another common example is "RAM memory", which is redundant because "RAM" ("random-access memory") includes the initial of the word "memory". "PIN" stands for "personal identification number", obviating the second word in "PIN number"; in this case its retention may be motivated to avoid ambiguity with the homophonous word "pin". Other examples include "ATM machine" ("automated teller machine machine"), "EAB bank" ("European American Bank bank"), "CableACE Award" ("cable award for cable excellence award"), "DC Comics" ("Detective Comics Comics"), "HIV virus" ("human immunodeficiency virus virus"), Microsoft's NT Technology ("New Technology Technology") and the formerly redundant "SAT test" ("Scholastic Achievement/Aptitude/Assessment Test test", now simply "SAT Reasoning Test"). TNN (The Nashville/National Network) also renamed itself "The New TNN" for a brief interlude.

Simple redefining

Sometimes, the initials continue to stand for an expanded meaning, but the original meaning is simply replaced. Some examples:
*DVD was originally an acronym of the unofficial term digital video disk, but is now stated by the DVD Forum as standing for Digital Versatile Disc.
*GAO changed the full form of its name from General Accounting Office to Government Accountability Office.
*GPO changed the full form of its name from Government Printing Office to Government Publishing Office.
*RAID used to mean Redundant Array of Inexpensive Disks, but is now commonly interpreted as Redundant Array of Independent Disks.
*WWF originally stood for World Wildlife Fund, but now stands for Worldwide Fund for Nature (although the former name is still used in Canada and the United States).
*The UICC, whose initials came from the Romance-language versions of its name (such as French ', "International Union Against Cancer"), changed the English expansion of its name to Union for International Cancer Control (from International Union Against Cancer) so that the English expansion, too, would correspond to the UICC initials.

Backronyms

A backronym (or bacronym) is a phrase that is constructed "after the fact" from a previously existing word. For example, the novelist and critic Anthony Burgess once proposed that the word "book" ought to stand for "Box Of Organized Knowledge."  A classic real-world example of this is the name of the predecessor to the Apple Macintosh, The Apple Lisa, which was said to refer to "Local Integrated Software Architecture", but was actually named after Steve Jobs' daughter, born in 1978.

Contrived acronyms

Acronyms are sometimes contrived, that is, deliberately designed to be especially apt for the thing being named (by having a dual meaning or by borrowing the positive connotations of an existing word). Some examples of contrived acronyms are USA PATRIOT, CAN SPAM, CAPTCHA and ACT UP. The clothing company French Connection began referring to itself as fcuk, standing for "French Connection United Kingdom." The company then created T-shirts and several advertising campaigns that exploit the acronym's similarity to the taboo word "fuck."

The US Department of Defense's Defense Advanced Research Projects Agency (DARPA) is known for developing contrived acronyms to name projects, including RESURRECT, NIRVANA, and DUDE. In July 2010, Wired Magazine reported that DARPA announced programs to "..transform biology from a descriptive to a predictive field of science" named BATMAN and ROBIN for Biochronicity and Temporal Mechanisms Arising in Nature and Robustness of Biologically-Inspired Networks,  a reference to the Batman and Robin comic-book superheroes.

Some acronyms are chosen deliberately to avoid a name considered undesirable: For example, Verliebt in Berlin (ViB), a German telenovela, was first intended to be Alles nur aus Liebe (All for Love), but was changed to avoid the resultant acronym ANAL. Likewise, the Computer Literacy and Internet Technology qualification is known as CLaIT,  rather than CLIT. In Canada, the Canadian Conservative Reform Alliance (Party) was quickly renamed to the Canadian Reform Conservative Alliance when its opponents pointed out that its initials spelled CCRAP (pronounced "see crap"). (The satirical magazine Frank had proposed alternatives to CCRAP, namely SSHIT and NSDAP.) Two Irish Institutes of Technology (Galway and Tralee) chose different acronyms from other institutes when they were upgraded from Regional Technical colleges. Tralee RTC became the Institute of Technology Tralee (ITT), as opposed to Tralee Institute of Technology (TIT). Galway RTC became Galway-Mayo Institute of Technology (GMIT), as opposed to Galway Institute of Technology (GIT). The charity sports organization Team in Training is known as "TNT" and not "TIT". Technological Institute of Textile & Sciences is still known as TITS. George Mason University was planning to name their law school the Antonin Scalia School of Law (ASSOL) in honor of the late Antonin Scalia, only to change it to the Antonin Scalia Law School later. 

Macronyms/nested acronyms

A macronym, or nested acronym, is an acronym in which one or more letters stand for acronyms themselves. The word "macronym" is a portmanteau of "macro-" and "acronym".

Some examples of macronyms are: 
* XHR stands for "XML HTTP Request", in which XML is "eXtensible Markup Language", and HTTP stands for "HyperText Transfer Protocol".
* POWER stands for Performance Optimization With Enhanced RISC, in which RISC stands for Reduced Instruction Set Computing.
* VHDL stands for "VHSIC Hardware Description Language", in which VHSIC stands for "Very High Speed Integrated Circuit".
* XSD stands for "XML Schema Definition", in which XML stands for "eXtensible Markup Language".
* SECS stands for "SEMI equipment communication standard", in which SEMI stands for "Semiconductor equipment manufacturing industries".
* AIM stands for "AOL Instant Messenger", in which AOL stands for "America Online".
* HASP stood for Houston Automatic Spooling Priority, but spooling itself was an acronym – simultaneous peripheral operations on-line

Some macronyms can be multiply nested: the second-order acronym points to another one further down a hierarchy. In an informal competition run by the magazine New Scientist, a fully documented specimen was discovered that may be the most deeply nested of all: RARS is the "Regional ATOVS Retransmission Service", ATOVS is "Advanced TOVS", TOVS is "TIROS operational vertical sounder" and TIROS is "Television infrared observational satellite". Fully expanded, "RARS" thus becomes: "Regional Advanced Television Infrared Observational Satellite Operational Vertical Sounder Retransmission Service".

Recursive acronyms

A special type of macronym, the recursive acronym, has letters whose expansion refers back to the macronym itself. One of the earliest examples appears in The Hacker's Dictionary as MUNG, which stands for "MUNG Until No Good".

Some examples of recursive acronyms are:
* GNU stands for "GNU's Not Unix"
* LAME stands for "LAME Ain't an MP3 Encoder"
* PHP stands for "PHP: Hypertext Preprocessor"
* WINE stands for "WINE Is Not an Emulator"
* HURD stands for "HIRD of Unix-replacing daemons", where HIRD itself stands for "HURD of interfaces representing depth" (a "mutually recursive" acronym)

Non-English languages

Specific languages

Chinese

In English language discussions of languages with syllabic or logographic writing systems (such as Chinese, Japanese, and Korean), "acronyms" describe the short forms that take selected characters from a multi-character word.

For example, in Chinese, "university" (/, literally "great learning") is usually abbreviated simply as  ("great") when used with the name of the institute. So Peking University () is commonly shortened to  ( "north-great") by also only taking the first character of Peking, the "northern capital" (). In some cases, however, other characters than the first can be selected. For example, the local short form of Hong Kong University () uses Kong () rather than Hong.

There are also cases where some longer phrases are abbreviated drastically, especially in Chinese politics, where proper nouns were initially translated from Soviet Leninist terms. For instance, the full name of China's highest ruling council, the Politburo Standing Committee (PSC), is "Standing Committee of the Central Political Bureau of the Communist Party of China" (中国共产党中央政治局常务委员会). The term then reduced the "Communist Party of China" part of its name through acronyms, then the "Standing Committee" part, again through acronyms, to create "中共中央政治局常委". Alternatively, it omitted the "Communist Party" part altogether, creating "Politburo Standing Committee" (政治局常委会), and eventually just "Standing Committee" (常委会). The PSC's members full designations are "Member of the Standing Committee of the Central Political Bureau of the Communist Party of China" (中国共产党中央政治局常务委员会委员); this was eventually drastically reduced to simply Changwei (常委), with the term Ruchang (入常) used increasingly for officials destined for a future seat on the PSC. In another example, the word "全国人民代表大会" (National People's Congress) can be broken into four parts: "全国" "the whole nation", "人民" 
 "people", "代表" "representatives", "大会" 
 "conference". Yet, in its short form "人大" (literally "man/people big"), only the first characters from the second and the fourth parts are selected; the first part ("全国") and the third part ("代表") are simply ignored. In describing such abbreviations, the term initialism is inapplicable.

Many proper nouns become shorter and shorter over time. For example, the CCTV New Year's Gala, whose full name is literally read as "China Central Television Spring Festival Joint Celebration Evening Gala" (中国中央电视台春节联欢晚会) was first shortened to "Spring Festival Joint Celebration Evening Gala" (春节联欢晚会), but eventually referred to as simply Chunwan (春晚). Along the same vein, Zhongguo Zhongyang Dianshi Tai (中国中央电视台) was reduced to Yangshi (央视) in the mid-2000s.

Korean

Many aspects of academics in Korea follow similar acronym patterns as Chinese, owing to the languages' commonalities, like using the word for "big" or "great" i.e. dae (), to refer to universities (; daehak, literally "great learning" although "big school" is an acceptable alternate). They can be interpreted similar to American university appellations, such as "UPenn" or "Texas Tech."

Some acronyms are shortened forms of the school's name, like how Hongik University (, Hongik Daehakgyo) is shortened to Hongdae (, "Hong, the big [school]" or "Hong-U") Other acronyms can refer to the university's main subject, e.g. Korea National University of Education (, Hanguk Gyowon Daehakgyo) is shortened to Gyowondae (교원대, "Big Ed." or "Ed.-U"). Other schools use a Koreanized version of their English acronym. The Korea Advanced Institute of Science and Technology (, Hanguk Gwahak Gisulwon) is referred to as KAIST (, Kaiseuteu) in both English and Korean. The 3 most prestigious schools in Korea are known as SKY (스카이, seukai), combining the first letter of their English names (Seoul National, Korea, and Yonsei Universities). In addition, the College Scholastic Ability Test (, Daehak Suhang Neungryeok Siheom) is shortened to Suneung (, "S.A.").

Japanese

The Japanese language makes extensive use of acronyms. This is most prevalent in katakana transcriptions of foreign words; for example, the Pokémon media franchise's name originally stood for "pocket monsters" ( → ), which is still the long-form of the name in Japanese, and "wāpuro" stands for "word processor" ( → ). However, the practice is also common with native kanji and hiragana words.

German

To a greater degree than English does, German tends toward acronyms that use initial syllables rather than initial single letters, although it uses many of the latter type as well. Some examples of the syllabic type are Gestapo rather than GSP (for ', 'secret state police'); ' rather than FAK (for ', anti-aircraft gun); ' rather than KP (for ', detective division police). The extension of such contraction to a pervasive or whimsical degree has been mockingly labeled ' (for ', strange habit of abbreviating). Examples of  include ' (for ', short in the front, long in the back, i.e., a mullet) and the mocking of Adolf Hitler's title as ' (', Greatest General of all Times).

Hebrew

It is common to take more than just one initial letter from each of the words composing the acronym; regardless of this, the abbreviation sign gershayim is always written between the second-last and last letters of the non-inflected form of the acronym, even if by this it separates letters of the same original word.  Examples (keep in mind Hebrew reads right-to-left):  (for , the United States);  (for , the Soviet Union);  (for , Rishon LeZion);  (for , the school). An example that takes only the initial letters from its component words is  (Tzahal, for , Israel Defense Forces). In inflected forms the abbreviation sign gershayim remains between the second-last and last letters of the non-inflected form of the acronym (e.g. "report", singular: , plural: ; "squad commander", masculine: , feminine: ).

Indonesian

There is also a widespread use of acronyms in Indonesia in every aspect of social life. For example, the Golkar political party stands for Partai Golongan Karya, Monas stands for "Monumen Nasional" (National Monument), the Angkot public transport stands for "Angkutan Kota" (city public transportation), warnet stands for "warung internet" (internet cafe), and many others. Some acronyms are considered formal (or officially adopted), while many more are considered informal, slang or colloquial.

The capital's metropolitan area (Jakarta and its surrounding satellite regions), Jabodetabek, is another infamous acronym. This stands for Jakarta-Bogor-Depok-Tangerang-Bekasi. Many highways are also named by the acronym method; e.g. Jalan Tol (Toll Road) Jagorawi (Jakarta-Bogor-Ciawi) and Purbaleunyi (Purwakarta-Bandung-Cileunyi), Joglo Semar (Jogja-solo-semarang).

In some languages, especially those that use certain alphabets, many acronyms come from the governmental use, particularly in the military and law enforcement services. The Indonesian military (TNI—Tentara Nasional Indonesia) and Indonesian police (POLRI—Kepolisian Republik Indonesia) are infamous for heavy acronyms use. Examples include the Kopassus (Komando Pasukan Khusus; Special Forces Command), Kopaska (Komando Pasukan Katak; Frogmen Command), Kodim (Komando Distrik Militer; Military District Command—one of the Indonesian army's administrative divisions), Serka (Sersan Kepala; Head Sergeant), Akmil (Akademi Militer; Military Academy—in Magelang) and many other terms regarding ranks, units, divisions, procedures, etc.

Heavy acronym use by Indonesians, makes it difficult for foreigners and learners of Bahasa Indonesia to seek information and news in Indonesian media.

Russian

Acronyms that use parts of words (not necessarily syllables) are commonplace in Russian as well, e.g.  (Gazprom), for  (', gas industry). There are also initialisms, such as СМИ (SMI, for  ', means of mass informing, i.e. mass media). Another Russian acronym,  (GULag) combines two initials and three letters of the final word: it stands for  (', Chief Administration of Camps).

Historically, OTMA was an acronym sometimes used by the daughters of Emperor Nicholas II of Russia and his consort, Alexandra Feodorovna, as a group nickname for themselves, built from the first letter of each girl's name in the order of their births : Olga, Tatiana, Maria and Anastasia.

Swahili

In Swahili, acronyms are common for naming organizations such as TUKI, which stands for ' (the Institute for Swahili Research). Multiple initial letters (often the initial syllable of words) are often drawn together, as seen more in some languages than others.

General grammatical considerations

Declension

In languages where nouns are declined, various methods are used. An example is Finnish, where a colon is used to separate inflection from the letters:
*An acronym is pronounced as a word: Nato—' "into Nato"
*An acronym is pronounced as letters: EU—' "into EU"
*An acronym is interpreted as words: EU—' "into EU"
The process above is similar to how, in English, hyphens are used for clarity when prefixes are added to acronyms, thus pre-NATO policy (rather than preNATO).

Lenition

In languages such as Scottish Gaelic and Irish, where lenition (initial consonant mutation) is commonplace, acronyms must also be modified in situations where case and context dictate it. In the case of Scottish Gaelic, a lower case "h" is added after the initial consonant; for example, BBC Scotland in the genitive case would be written as BhBC Alba, with the acronym pronounced "VBC". Likewise, the Gaelic acronym for "television" (gd: telebhisean) is TBh, pronounced "TV", as in English.

Extremes

*The longest acronym, according to the 1965 edition of Acronyms, Initialisms and Abbreviations Dictionary, is ADCOMSUBORDCOMPHIBSPAC, a United States Navy term that stands for "Administrative Command, Amphibious Forces, Pacific Fleet Subordinate Command."  Another term COMNAVSEACOMBATSYSENGSTA, which stands for "Commander, Naval Sea Systems Combat Engineering Station" is longer but the word "Combat" is not shortened.
*The world's longest acronym, according to the Guinness Book of World Records is  (). The 56-letter acronym (54 in Cyrillic) is from the Concise Dictionary of Soviet Terminology and means "The laboratory for shuttering, reinforcement, concrete and ferroconcrete operations for composite-monolithic and monolithic constructions of the Department of the Technology of Building-assembly operations of the Scientific Research Institute of the Organization for building mechanization and technical aid of the Academy of Building and Architecture of the Union of Soviet Socialist Republics." ()
*The card-game Magic: The Gathering has a playing card called "Our Market Research Shows That Players Like Really Long Card Names So We Made this Card to Have the Absolute Longest Card Name Ever Elemental", with text on it saying: "Just call it OMRSTPLRLCNSWMTCTHTALCNEE for short."[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=74237 Our Market Research Shows That Players Like Really Long Card Names So We Made this Card to Have the Absolute Longest Card Name Ever Elemental (Unhinged) – Gatherer – Magic: Th...] A police force is a constituted body of persons empowered by the state to enforce the law, protect property, and limit civil disorder.  Their powers include the legitimized use of force. The term is most commonly associated with police services of a sovereign state that are authorized to exercise the police power of that state within a defined legal or territorial area of responsibility. Police forces are often defined as being separate from military or other organizations involved in the defense of the state against foreign aggressors; however, gendarmerie are military units charged with civil policing.

Law enforcement, however, constitutes only part of policing activity.  Policing has included an array of activities in different situations, but the predominant ones are concerned with the preservation of order.  In some societies, in the late 18th and early 19th centuries, these developed within the context of maintaining the class system and the protection of private property.  Many police forces suffer from police corruption to a greater or lesser degree. The police force is usually a public sector service, meaning they are paid through taxes.

Alternative names for police force include constabulary, gendarmerie, police department, police service, crime prevention, protective services, law enforcement agency, civil guard or civic guard. Members may be referred to as police officers, troopers, sheriffs, constables, rangers, peace officers or civic/civil guards.

As police are often interacting with individuals, slang terms are numerous. Many slang terms for police officers are decades or centuries old with lost etymology.

Etymology

First attested in English in the early 15th century, initially in a range of senses encompassing '(public) policy; state; public order', the word police comes from Middle French police ('public order, administration, government'),  in turn from Latin politia,  which is the Latinisation of the Greek πολιτεία (politeia), "citizenship, administration, civil polity".  This is derived from πόλις (polis), "city". 

History

Ancient policing

Law enforcement in ancient China was carried out by "prefects" for thousands of years since it developed in both the Chu and Jin kingdoms of the Spring and Autumn period. In Jin, dozens of prefects were spread across the state, each having limited authority and employment period. They were appointed by local magistrates, who reported to higher authorities such as governors, who in turn were appointed by the emperor, and they oversaw the civil administration of their "prefecture", or jurisdiction. Under each prefect were "subprefects" who helped collectively with law enforcement in the area. Some prefects were responsible for handling investigations, much like modern police detectives. Prefects could also be women.  The concept of the "prefecture system" spread to other cultures such as Korea and Japan.

In ancient Greece, publicly owned slaves were used by magistrates as police. In Athens, a group of 300 Scythian slaves (the , "rod-bearers") was used to guard public meetings to keep order and for crowd control, and also assisted with dealing with criminals, handling prisoners, and making arrests. Other duties associated with modern policing, such as investigating crimes, were left to the citizens themselves. 

In the Roman empire, the army, rather than a dedicated police organization, provided security. Local watchmen were hired by cities to provide some extra security. Magistrates such as procurators fiscal and quaestors investigated crimes. There was no concept of public prosecution, so victims of crime or their families had to organize and manage the prosecution themselves.

Under the reign of Augustus, when the capital had grown to almost one million inhabitants, 14 wards were created; the wards were protected by seven squads of 1,000 men called "vigiles", who acted as firemen and nightwatchmen. Their duties included apprehending thieves and robbers and capturing runaway slaves. The vigiles were supported by the Urban Cohorts who acted as a heavy-duty anti-riot force and even the Praetorian Guard if necessary.

Medieval policing

In medieval Spain, Santa Hermandades, or "(holy) brotherhoods", peacekeeping associations of armed individuals, were a characteristic of municipal life, especially in Castile. As medieval Spanish kings often could not offer adequate protection, protective municipal leagues began to emerge in the twelfth century against banditry and other rural criminals, and against the lawless nobility or to support one or another claimant to a crown.

These organizations were intended to be temporary, but became a long-standing fixture of Spain. The first recorded case of the formation of an hermandad occurred when the towns and the peasantry of the north united to police the pilgrim road to Santiago de Compostela in Galicia, and protect the pilgrims against robber knights.

Throughout the Middle Ages such alliances were frequently formed by combinations of towns to protect the roads connecting them, and were occasionally extended to political purposes. Among the most powerful was the league of North Castilian and Basque ports, the Hermandad de las marismas: Toledo, Talavera, and Villarreal.

As one of their first acts after end of the War of the Castilian Succession in 1479, Ferdinand II of Aragon and Isabella I of Castile established the centrally-organized and efficient Holy Brotherhood as a national police force. They adapted an existing brotherhood to the purpose of a general police acting under officials appointed by themselves, and endowed with great powers of summary jurisdiction even in capital cases. The original brotherhoods continued to serve as modest local police-units until their final suppression in 1835.

The Vehmic courts of Germany provided some policing in the absence of strong state institutions.

In France during the Middle Ages, there were two Great Officers of the Crown of France with police responsibilities: The Marshal of France and the Constable of France. The military policing responsibilities of the Marshal of France were delegated to the Marshal's provost, whose force was known as the Marshalcy because its authority ultimately derived from the Marshal. The marshalcy dates back to the Hundred Years' War, and some historians trace it back to the early 12th century. Another organisation, the Constabulary (French: Connétablie), was under the command of the Constable of France. The constabulary was regularised as a military body in 1337. Under Francis I of France (who reigned 1515–1547), the Maréchaussée was merged with the Constabulary. The resulting force was also known as the Maréchaussée, or, formally, the Constabulary and Marshalcy of France.

The English system of maintaining public order since the Norman conquest was a private system of tithings, led by a constable, which was based on a social obligation for the good conduct of the others; more common was that local lords and nobles were responsible for maintaining order in their lands, and often appointed a constable, sometimes unpaid, to enforce the law. There was also a system investigative "juries".

The Assize of Arms of 1252, which required the appointment of constables to summon men to arms, quell breaches of the peace, and to deliver offenders to the sheriffs or reeves, is cited as one of the earliest creation of the English police.  The Statute of Winchester of 1285 is also cited as the primary legislation regulating the policing of the country between the Norman Conquest and the Metropolitan Police Act 1829. 

From about 1500, private watchmen were funded by private individuals and organisations to carry out police functions. They were later nicknamed 'Charlies', probably after the reigning monarch King Charles II. Thief-takers were also rewarded for catching thieves and returning the stolen property.

The first use of the word police ("Polles") in English comes from the book "The Second Part of the Institutes of the Lawes of England" published in 1642. 

Early modern policing

The first centrally organised police force was created by the government of King Louis XIV in 1667 to police the city of Paris, then the largest city in Europe. The royal edict, registered by the Parlement of Paris on March 15, 1667 created the office of lieutenant général de police ("lieutenant general of police"), who was to be the head of the new Paris police force, and defined the task of the police as "ensuring the peace and quiet of the public and of private individuals, purging the city of what may cause disturbances, procuring abundance, and having each and everyone live according to their station and their duties".

This office was first held by Gabriel Nicolas de la Reynie, who had 44 commissaires de police (police commissioners) under his authority. In 1709, these commissioners were assisted by inspecteurs de police (police inspectors). The city of Paris was divided into 16 districts policed by the commissaires, each assigned to a particular district and assisted by a growing bureaucracy. The scheme of the Paris police force was extended to the rest of France by a royal edict of October 1699, resulting in the creation of lieutenants general of police in all large French cities and towns.

After the French Revolution, Napoléon I reorganized the police in Paris and other cities with more than 5,000 inhabitants on February 17, 1800 as the Prefecture of Police. On March 12, 1829, a government decree created the first uniformed police in France, known as sergents de ville ("city sergeants"), which the Paris Prefecture of Police's website claims were the first uniformed policemen in the world. 

In 1737, George II began paying some London and Middlesex watchmen with tax monies, beginning the shift to government control. In 1749 Henry Fielding began organizing a force of quasi-professional constables known as the Bow Street Runners. The Macdaniel affair added further impetus for a publicly salaried police force that did not depend on rewards. Nonetheless, In 1828, there were privately financed police units in no fewer than 45 parishes within a 10-mile radius of London.

The word "police" was borrowed from French into the English language in the 18th century, but for a long time it applied only to French and continental European police forces. The word, and the concept of police itself, were "disliked as a symbol of foreign oppression" (according to Britannica 1911). Before the 19th century, the first use of the word "police" recorded in government documents in the United Kingdom was the appointment of Commissioners of Police for Scotland in 1714 and the creation of the Marine Police in 1798.

Policing in London

In 1797, Patrick Colquhoun was able to persuade the West Indies merchants who operated at the Pool of London on the River Thames, to establish a police force at the docks to prevent rampant theft that was causing annual estimated losses of £500,000 worth of cargo.Dick Paterson, [http://www.thamespolicemuseum.org.uk/h_police_1.html Origins of the Thames Police], Thames Police Museum. Retrieved 4 February 2007. The idea of a police, as it then existed in France, was considered as a potentially undesirable foreign import. In building the case for the police in the face of England's firm anti-police sentiment, Colquhoun framed the political rationale on economic indicators to show that a police dedicated to crime prevention was "perfectly congenial to the principle of the British constitution." Moreover, he went so far as to praise the French system, which had reached "the greatest degree of perfection" in his estimation.T. A. Critchley, A History of Police in England and Wales, 2nd edition. Montclair, NJ: Patterson Smith, 38-39. 

 
With the initial investment of £4,200, the new trial force of the Thames River Police began with about 50 men charged with policing 33,000 workers in the river trades, of whom Colquhoun claimed 11,000 were known criminals and "on the game." The force was a success after its first year, and his men had "established their worth by saving £122,000 worth of cargo and by the rescuing of several lives." Word of this success spread quickly, and the government passed the Marine Police Bill on 28 July 1800, transforming it from a private to public police agency; now the oldest police force in the world. Colquhoun published a book on the experiment, The Commerce and Policing of the River Thames. It found receptive audiences far outside London, and inspired similar forces in other cities, notably, New York City, Dublin, and Sydney.

Colquhoun's utilitarian approach to the problem – using a cost-benefit argument to obtain support from businesses standing to benefit – allowed him to achieve what Henry and John Fielding failed for their Bow Street detectives. Unlike the stipendiary system at Bow Street, the river police were full-time, salaried officers prohibited from taking private fees.  His other contribution was the concept of preventive policing; his police were to act as a highly visible deterrent to crime by their permanent presence on the Thames. Colquhoun's innovations were a critical development leading up to Robert Peel's "new" police three decades later. 

Meanwhile, the authorities in Glasgow, Scotland successfully petitioned the government to pass the Glasgow Police Act establishing the City of Glasgow Police in 1800. Other Scottish towns soon followed suit and set up their own police forces through acts of parliament.  In Ireland, the Irish Constabulary Act of 1822 marked the beginning of the Royal Irish Constabulary. The Act established a force in each barony with chief constables and inspectors general under the control of the civil administration at Dublin Castle. By 1841 this force numbered over 8,600 men.

Metropolitan police force

London was fast reaching a size unprecedented in world history, due to the onset of the Industrial Revolution.  It became clear that the locally maintained system of volunteer constables and "watchmen" was ineffective, both in detecting and preventing crime. A parliamentary committee was appointed to investigate the system of policing in London. Upon Sir Robert Peel being appointed as Home Secretary in 1822, he established a second and more effective committee, and acted upon its findings.

Royal assent to the Metropolitan Police Act 1829 was given  and the Metropolitan Police Service was established on September 29, 1829 in London as the first modern and professional police force in the world.   

Peel, widely regarded as the father of modern policing,  was heavily influenced by the social and legal philosophy of Jeremy Bentham, who called for a strong and centralized, but politically neutral, police force for the maintenance of social order, for the protection of people from crime and to act as a visible deterrent to urban crime and disorder. Peel decided to standardise the police force as an official paid profession, to organise it in a civilian fashion, and to make it answerable to the public. 

 
Due to public fears concerning the deployment of the military in domestic matters, Peel organised the force along civilian lines, rather than paramilitary. To appear neutral, the uniform was deliberately manufactured in blue, rather than red which was then a military colour, along with the officers being armed only with a wooden truncheon and a rattle to signal the need for assistance. Along with this, police ranks did not include military titles, with the exception of Sergeant. 

To distance the new police force from the initial public view of it as a new tool of government repression, Peel publicised the so-called Peelian principles, which set down basic guidelines for ethical policing:

* Every police officer should be issued an warrant card with a unique identification number to assure accountability for his actions.
* Whether the police are effective is not measured on the number of arrests but on the lack of crime.
* Above all else, an effective authority figure knows trust and accountability are paramount. Hence, Peel's most often quoted principle that "The police are the public and the public are the police."

The 1829 Metropolitan Police Act created a modern police force by limiting the purview of the force and its powers, and envisioning it as merely an organ of the judicial system. Their job was apolitical; to maintain the peace and apprehend criminals for the courts to process according to the law.  This was very different to the "continental model" of the police force that had been developed in France, where the police force worked within the parameters of the absolutist state as an extension of the authority of the monarch and functioned as part of the governing state.

In 1863, the Metropolitan Police were issued with the distinctive custodian helmet, and in 1884 they switched to the use of whistles that could be heard from much further away.  The Metropolitan Police became a model for the police forces in most countries, such as the United States, and most of the British Empire. Bobbies can still be found in many parts of the Commonwealth of Nations. 

Other countries

Australia

In Australia the first police force having centralised command as well as jurisdiction over an entire colony was the South Australia Police, formed in 1838 under Henry Inman.

However, whilst the New South Wales Police Force was established in 1862, it was made up from a large number of policing and military units operating within the then Colony of New South Wales and traces its links back to the Royal Marines. The passing of the Police Regulation Act of 1862 essentially tightly regulated and centralised all of the police forces operating throughout the Colony of New South Wales.

The New South Wales Police Force remains the largest police force in Australia in terms of personnel and physical resources. It is also the only police force that requires its recruits to undertake university studies at the recruit level and has the recruit pay for their own education.

Brazil

In 1566, the first police investigator of Rio de Janeiro was recruited. By the 17th century, most captaincies already had local units with law enforcement functions. On July 9, 1775 a Cavalry Regiment was created in the state of Minas Gerais for maintaining law and order. In 1808, the Portuguese royal family relocated to Brazil, because of the French invasion of Portugal. King João VI established the "Intendência Geral de Polícia" (General Police Intendancy) for investigations. He also created a Royal Police Guard for Rio de Janeiro in 1809. In 1831, after independence, each province started organizing its local "military police", with order maintenance tasks. The Federal Railroad Police was created in 1852.

Canada

In Canada, the Royal Newfoundland Constabulary was founded in 1729, making it the first police force in present-day Canada. It was followed in 1834 by the Toronto Police, and in 1838 by police forces in Montreal and Quebec City. A national force, the Dominion Police, was founded in 1868. Initially the Dominion Police provided security for parliament, but its responsibilities quickly grew. The famous Royal Northwest Mounted Police was founded in 1873.
The merger of these two police forces in 1920 formed the world-famous Royal Canadian Mounted Police.

Lebanon

In Lebanon, modern police were established in 1861, with creation of the Gendarmerie. 

India

In India, the police is under the control of respective States and union territories and is known to be under State Police Services (SPS). The candidates selected for the SPS are usually posted as Deputy Superintendent of Police or Assistant Commissioner of Police once their probationary period ends. On prescribed satisfactory service in the SPS, the officers are nominated to the Indian Police Service.[http://www.spiritofchennai.com/careerguide/ps.htm Police Service] The service color is usually dark blue and red, while the uniform color is Khaki. 

United States

In British North America, policing was initially provided by local elected officials. For instance, the New York Sheriff's Office was founded in 1626, and the Albany County Sheriff's Department in the 1660s. In the colonial period, policing was provided by elected sheriffs and local militias.

In 1789 the U.S. Marshals Service was established, followed by other federal services such as the U.S. Parks Police (1791)  and U.S. Mint Police (1792).  The first city police services were established in Philadelphia in 1751,  Richmond, Virginia in 1807,  Boston in 1838,  and New York in 1845.  The U.S. Secret Service was founded in 1865 and was for some time the main investigative body for the federal government. 

In the American Old West, policing was often of very poor quality. The Army often provided some policing alongside poorly resourced sheriffs and temporarily organized posses. Public organizations were supplemented by private contractors, notably the Pinkerton National Detective Agency, which was hired by individuals, businessmen, local governments and the federal government. At its height, the Pinkerton Agency's numbers exceeded those of the United States Army.

In recent years, in addition to federal, state, and local forces, some special districts have been formed to provide extra police protection in designated areas. These districts may be known as neighborhood improvement districts, crime prevention districts, or security districts. 

In 2005, the Supreme Court of the United States ruled that police do not have a constitutional duty to protect a person from harm. 

Development of theory

Michel Foucault claims that the contemporary concept of police as a paid and funded functionary of the state was developed by German and French legal scholars and practitioners in Public administration and Statistics in the 17th and early 18th centuries, most notably with Nicolas Delamare's [http://cujas.synasoft.fr/page.asp?Ouvrage225&Ftime
1 Traité de la Police] ("Treatise on the Police"), first published in 1705. The German Polizeiwissenschaft (Science of Police) first theorized by Philipp von Hörnigk a 17th-century Austrian Political economist and civil servant and much more famously by Johann Heinrich Gottlob Justi who produced an important theoretical work known as Cameral science on the formulation of police.  Foucault cites Magdalene Humpert author of Bibliographie der Kameralwissenschaften (1937) in which the author makes note of a substantial bibliography was produced of over 4000 pieces of the practice of Polizeiwissenschaft however, this maybe a mistranslation of Foucault's own work the actual source of Magdalene Humpert states over 14,000 items were produced from the 16th century dates ranging from 1520-1850.  

As conceptualized by the Polizeiwissenschaft,according to Foucault the police had an administrative,economic and social duty ("procuring abundance"). It was in charge of demographic concerns and needed to be incorporated within the western political philosophy system of raison d'état and therefore giving the superficial appearance of empowering the population (and unwittingly supervising the population), which, according to mercantilist theory, was to be the main strength of the state. Thus, its functions largely overreached simple law enforcement activities and included public health concerns, urban planning (which was important because of the miasma theory of disease; thus, cemeteries were moved out of town, etc.), and surveillance of prices. 

The concept of preventive policing, or policing to deter crime from taking place, gained influence in the late 18th century. Police Magistrate John Fielding, head of the Bow Street Runners, argued that "...it is much better to prevent even one man from being a rogue than apprehending and bringing forty to justice." 

The Utilitarian philosopher, Jeremy Bentham, promoted the views of Italian Marquis Cesare Beccaria, and disseminated a translated version of "Essay on Crime in Punishment". Bentham espoused the guiding principle of "the greatest good for the greatest number:
:It is better to prevent crimes than to punish them. This is the chief aim of every good system of legislation, which is the art of leading men to the greatest possible happiness or to the least possible misery, according to calculation of all the goods and evils of life.

Patrick Colquhoun's influential work, A Treatise on the Police of the Metropolis (1797) was heavily influenced by Benthamite thought. Colquhoun's Thames River Police was founded on these principles, and in contrast to the Bow Street Runners, acted as a deterrent by their continual presence on the riverfront, in addition to being able to intervene if they spotted a crime in progress. 

Edwin Chadwick's 1829 article, "Preventive police" in the London Review,  argued that prevention ought to be the primary concern of a police body, which was not the case in practice. The reason, argued Chadwick, was that "A preventive police would act more immediately by placing difficulties in obtaining the objects of temptation." In contrast to a deterrent of punishment, a preventive police force would deter criminality by making crime cost-ineffective - "crime doesn't pay". In the second draft of his 1829 Police Act, the "object" of the new Metropolitan Police, was changed by Robert Peel to the "principal object," which was the "prevention of crime."  Later historians would attribute the perception of England's "appearance of orderliness and love of public order" to the preventive principle entrenched in Peel's police system. 

Development of modern police forces around the world was contemporary to the formation of the state, later defined by sociologist Max Weber as achieving a "monopoly on the legitimate use of physical force" and which was primarily exercised by the police and the military. Marxist theory situates the development of the modern state as part of the rise of capitalism, in which the police are one component of the bourgeoisie's repressive apparatus for subjugating the working class.

Personnel and organization

Police forces include both preventive (uniformed) police and detectives. Terminology varies from country to country. Police functions include protecting life and property, enforcing criminal law, criminal investigations, regulating traffic, crowd control, and other public safety duties.

Uniformed police

Preventive Police, also called Uniform Branch, Uniformed Police, Uniform Division, Administrative Police, Order Police, or Patrol, designates the police that patrol and respond to emergencies and other incidents, as opposed to detective services. As the name "uniformed" suggests, they wear uniforms and perform functions that require an immediate recognition of an officer's legal authority, such as traffic control, stopping and detaining motorists, and more active crime response and prevention.

Preventive police almost always make up the bulk of a police service's personnel. In Australia and Britain, patrol personnel are also known as "general duties" officers.  Atypically, Brazil's preventive police are known as Military Police. 

Detectives

Police detectives are responsible for investigations and detective work. Detectives may be called Investigations Police, Judiciary/Judicial Police, and Criminal Police. In the UK, they are often referred to by the name of their department, the Criminal Investigation Department (CID). Detectives typically make up roughly 15%-25% of a police service's personnel.

Detectives, in contrast to uniformed police, typically wear 'business attire' in bureaucratic and investigative functions where a uniformed presence would be either a distraction or intimidating, but a need to establish police authority still exists. "Plainclothes" officers dress in attire consistent with that worn by the general public for purposes of blending in.

In some cases, police are assigned to work "undercover", where they conceal their police identity to investigate crimes, such as organized crime or narcotics crime, that are unsolvable by other means. In some cases this type of policing shares aspects with espionage.

Despite popular conceptions promoted by movies and television, many US police departments prefer not to maintain officers in non-patrol bureaus and divisions beyond a certain period of time, such as in the detective bureau, and instead maintain policies that limit service in such divisions to a specified period of time, after which officers must transfer out or return to patrol duties. This is done in part based upon the perception that the most important and essential police work is accomplished on patrol in which officers become acquainted with their beats, prevent crime by their presence, respond to crimes in progress, manage crises, and practice their skills.

Detectives, by contrast, usually investigate crimes after they have occurred and after patrol officers have responded first to a situation. Investigations often take weeks or months to complete, during which time detectives spend much of their time away from the streets, in interviews and courtrooms, for example. Rotating officers also promotes cross-training in a wider variety of skills, and serves to prevent "cliques" that can contribute to corruption or other unethical behavior.

Auxiliary

Police may also take on auxiliary administrative duties, such as issuing firearms licenses. The extent that police have these functions varies among countries, with police in France, Germany, and other continental European countries handling such tasks to a greater extent than British counterparts.

Specialized units

Specialized preventive and detective groups, or Specialist Investigation Departments exist within many law enforcement organizations either for dealing with particular types of crime, such as traffic law enforcement and crash investigation, homicide, or fraud; or for situations requiring specialized skills, such as underwater search, aviation, explosive device disposal ("bomb squad"), and computer crime.

Most larger jurisdictions also employ specially selected and trained quasi-military units armed with military-grade weapons for the purposes of dealing with particularly violent situations beyond the capability of a patrol officer response, including high-risk warrant service and barricaded suspects. In the United States these units go by a variety of names, but are commonly known as SWAT (Special Weapons And Tactics) teams.

In counterinsurgency-type campaigns, select and specially trained units of police armed and equipped as light infantry have been designated as police field forces who perform paramilitary-type patrols and ambushes whilst retaining their police powers in areas that were highly dangerous. 

Because their situational mandate typically focuses on removing innocent bystanders from dangerous people and dangerous situations, not violent resolution, they are often equipped with non-lethal tactical tools like chemical agents, "flashbang" and concussion grenades, and rubber bullets. The London Metropolitan police's Specialist Firearms Command (CO19)  is a group of armed police used in dangerous situations including hostage taking, armed robbery/assault and terrorism.

Military police

Military police may refer to:
* a section of the military solely responsible for policing the armed forces (referred to as provosts)
* a section of the military responsible for policing in both the armed forces and in the civilian population (most gendarmeries, such as the French Gendarmerie, the Italian Carabinieri, the Spanish Guardia Civil and the Portuguese Republican National Guard also known as GNR)
* a section of the military solely responsible for policing the civilian population (such as the Romanian Gendarmerie)
* the civilian preventive police of a Brazilian state (Policia Militar)
* a Special Military law enforcement Service, like the Russian Military Police

Religious police

Some Islamic societies have religious police, who enforce the application of Islamic Sharia law. Their authority may include the power to arrest unrelated men and women caught socializing, anyone engaged in homosexual behavior or prostitution; to enforce Islamic dress codes, and store closures during Islamic prayer time.  

They enforce Muslim dietary laws, prohibit the consumption or sale of alcoholic beverages and pork, and seize banned consumer products and media regarded as un-Islamic, such as CDs/DVDs of various Western musical groups, television shows and film. In Saudi Arabia, the Mutaween actively prevent the practice or proselytizing of non-Islamic religions within Saudi Arabia, where they are banned.

Varying jurisdictions

Police forces are usually organized and funded by some level of government. The level of government responsible for policing varies from place to place, and may be at the national, regional or local level. In some places there may be multiple police forces operating in the same area, with different ones having jurisdiction according to the type of crime or other circumstances.

For example, in the UK, policing is primarily the responsibility of a regional police force; however specialist units exist at the national level. In the US, there is typically a state police force, but crimes are usually handled by local police forces that usually only cover a few municipalities. National agencies, such as the FBI, only have jurisdiction over federal crimes or those with an interstate component.

In addition to conventional urban or regional police forces, there are other police forces with specialized functions or jurisdiction. In the United States, the federal government has a number of police forces with their own specialized jurisdictions.

Some examples are the Federal Protective Service, which patrols and protects government buildings; the postal police, which protect postal buildings, vehicles and items; the Park Police, which protect national parks, or Amtrak Police which patrol Amtrak stations and trains.

There are also some government agencies that perform police functions in addition to other duties. The U.S. Coast Guard carries out many police functions for boaters.

In major cities, there may be a separate police agency for public transit systems, such as the New York City Port Authority Police or the MTA police, or for major government functions, such as sanitation, or environmental functions.

International policing

The terms international policing, transnational policing, and/or global policing began to be used from the early 1990s onwards to describe forms of policing that transcended the boundaries of the sovereign nation-state (Nadelmann, 1993),  (Sheptycki, 1995).  These terms refer in variable ways to practices and forms for policing that, in some sense, transcend national borders. This includes a variety of practices, but international police cooperation, criminal intelligence exchange between police agencies working in different nation-states, and police development-aid to weak, failed or failing states are the three types that have received the most scholarly attention.

Historical studies reveal that policing agents have undertaken a variety of cross-border police missions for many years (Deflem, 2002).  For example, in the 19th century a number of European policing agencies undertook cross-border surveillance because of concerns about anarchist agitators and other political radicals. A notable example of this was the occasional surveillance by Prussian police of Karl Marx during the years he remained resident in London. The interests of public police agencies in cross-border co-operation in the control of political radicalism and ordinary law crime were primarily initiated in Europe, which eventually led to the establishment of Interpol before the Second World War. There are also many interesting examples of cross-border policing under private auspices and by municipal police forces that date back to the 19th century (Nadelmann, 1993). It has been established that modern policing has transgressed national boundaries from time to time almost from its inception. It is also generally agreed that in the post–Cold War era this type of practice became more significant and frequent (Sheptycki, 2000). 

Not a lot of empirical work on the practices of inter/transnational information and intelligence sharing has been undertaken. A notable exception is James Sheptycki's study of police cooperation in the English Channel region (2002),  which provides a systematic content analysis of information exchange files and a description of how these transnational information and intelligence exchanges are transformed into police case-work. The study showed that transnational police information sharing was routinized in the cross-Channel region from 1968 on the basis of agreements directly between the police agencies and without any formal agreement between the countries concerned. By 1992, with the signing of the Schengen Treaty, which formalized aspects of police information exchange across the territory of the European Union, there were worries that much, if not all, of this intelligence sharing was opaque, raising questions about the efficacy of the accountability mechanisms governing police information sharing in Europe (Joubert and Bevers, 1996). 

Studies of this kind outside of Europe are even rarer, so it is difficult to make generalizations, but one small-scale study that compared transnational police information and intelligence sharing practices at specific cross-border locations in North America and Europe confirmed that low visibility of police information and intelligence sharing was a common feature (Alain, 2001).  Intelligence-led policing is now common practice in most advanced countries (Ratcliffe, 2007)  and it is likely that police intelligence sharing and information exchange has a common morphology around the world (Ratcliffe, 2007). James Sheptycki has analyzed the effects of the new information technologies on the organization of policing-intelligence and suggests that a number of 'organizational pathologies' have arisen that make the functioning of security-intelligence processes in transnational policing deeply problematic. He argues that transnational police information circuits help to "compose the panic scenes of the security-control society".  The paradoxical effect is that, the harder policing agencies work to produce security, the greater are feelings of insecurity.

Police development-aid to weak, failed or failing states is another form of transnational policing that has garnered attention. This form of transnational policing plays an increasingly important role in United Nations peacekeeping and this looks set to grow in the years ahead, especially as the international community seeks to develop the rule of law and reform security institutions in States recovering from conflict (Goldsmith and Sheptycki, 2007)  With transnational police development-aid the imbalances of power between donors and recipients are stark and there are questions about the applicability and transportability of policing models between jurisdictions (Hills, 2009). 

Perhaps the greatest question regarding the future development of transnational policing is: in whose interest is it? At a more practical level, the question translates into one about how to make transnational policing institutions democratically accountable (Sheptycki, 2004).  For example, according to the Global Accountability Report for 2007 (Lloyd, et al. 2007) Interpol had the lowest scores in its category (IGOs), coming in tenth with a score of 22% on overall accountability capabilities (p. 19).  As this report points out, and the existing academic literature on transnational policing seems to confirm, this is a secretive area and one not open to civil society involvement.

Equipment

Weapons

In many jurisdictions, police officers carry firearms, primarily handguns, in the normal course of their duties. In the United Kingdom (except Northern Ireland), Iceland, Ireland, Norway, New Zealand,  and Malta, with the exception of specialist units, officers do not carry firearms as a matter of course.

Police often have specialist units for handling armed offenders, and similar dangerous situations, and can (depending on local laws), in some extreme circumstances, call on the military (since Military Aid to the Civil Power is a role of many armed forces). Perhaps the most high-profile example of this was, in 1980 the Metropolitan Police handing control of the Iranian Embassy Siege to the Special Air Service.

They can also be armed with non-lethal (more accurately known as "less than lethal" or "less-lethal") weaponry, particularly for riot control. Non-lethal weapons include batons, tear gas, riot control agents, rubber bullets, riot shields, water cannons and electroshock weapons. Police officers often carry handcuffs to restrain suspects. The use of firearms or deadly force is typically a last resort only to be used when necessary to save human life, although some jurisdictions (such as Brazil) allow its use against fleeing felons and escaped convicts. A "shoot-to-kill" policy was recently introduced in South Africa, which allows police to use deadly force against any person who poses a significant threat to them or civilians.  With the country having one of the highest rates of violent crime, president Jacob Zuma states that South Africa needs to handle crime differently from other countries. 

Communications

Modern police forces make extensive use of radio communications equipment, carried both on the person and installed in vehicles, to co-ordinate their work, share information, and get help quickly. In recent years, vehicle-installed computers have enhanced the ability of police communications, enabling easier dispatching of calls, criminal background checks on persons of interest to be completed in a matter of seconds, and updating officers' daily activity log and other, required reports on a real-time basis. Other common pieces of police equipment include flashlights/torches, whistles, police notebooks and "ticket books" or citations.

Vehicles

Police vehicles are used for detaining, patrolling and transporting. The average police patrol vehicle is a specially modified, four door sedan (saloon in British English). Police vehicles are usually marked with appropriate logos and are equipped with sirens and flashing light bars to aid in making others aware of police presence.

Unmarked vehicles are used primarily for sting operations or apprehending criminals without alerting them to their presence. Some police forces use unmarked or minimally marked cars for traffic law enforcement, since drivers slow down at the sight of marked police vehicles and unmarked vehicles make it easier for officers to catch speeders and traffic violators. This practice is controversial, with for example, New York State banning this practice in 1996 on the grounds that it endangered motorists who might be pulled over by people impersonating police officers. 

Motorcycles are also commonly used, particularly in locations that a car may not be able to reach, to control potential public order situations involving meetings of motorcyclists and often in escort duties where motorcycle police officers can quickly clear a path for escorted vehicles. Bicycle patrols are used in some areas because they allow for more open interaction with the public. In addition, their quieter operation can facilitate approaching suspects unawares and can help in pursuing them attempting to escape on foot.

Police forces use an array of specialty vehicles such as helicopters, airplanes, watercraft, mobile command posts, vans, trucks, all-terrain vehicles, motorcycles, and armored vehicles.

Other safety equipment

Police cars may also contain fire extinguishers   or defibrillators. 

Strategies

The advent of the police car, two-way radio, and telephone in the early 20th century transformed policing into a reactive strategy that focused on responding to calls for service.  With this transformation, police command and control became more centralized.

In the United States, August Vollmer introduced other reforms, including education requirements for police officers.  O.W. Wilson, a student of Vollmer, helped reduce corruption and introduce professionalism in Wichita, Kansas, and later in the Chicago Police Department.  Strategies employed by O.W. Wilson included rotating officers from community to community to reduce their vulnerability to corruption, establishing of a non-partisan police board to help govern the police force, a strict merit system for promotions within the department, and an aggressive recruiting drive with higher police salaries to attract professionally qualified officers.  During the professionalism era of policing, law enforcement agencies concentrated on dealing with felonies and other serious crime, rather than broader focus on crime prevention. 

The Kansas City Preventive Patrol study in the 1970s found this approach to policing to be ineffective. Patrol officers in cars were disconnected from the community, and had insufficient contact and interaction with the community.  In the 1980s and 1990s, many law enforcement agencies began to adopt community policing strategies, and others adopted problem-oriented policing.

Broken windows policing was another, related approach introduced in the 1980s by James Q. Wilson and George L. Kelling, who suggested that police should pay greater attention to minor "quality of life" offenses and disorderly conduct. This method was first introduced and made popular by New York City Mayor, Rudy Giuliani, in the early 1990s.

The concept behind this method is simple: broken windows, graffiti, and other physical destruction or degradation of property, greatly increases the chances of more criminal activities and destruction of property. When criminals see the abandoned vehicles, trash, and deplorable property, they assume that authorities do not care and do not take active approaches to correct problems in these areas. Therefore, correcting the small problems prevents more serious criminal activity. 

Building upon these earlier models, intelligence-led policing has emerged as the dominant philosophy guiding police strategy. Intelligence-led policing and problem-oriented policing are complementary strategies, both which involve systematic use of information.  Although it still lacks a universally accepted definition, the crux of intelligence-led policing is an emphasis on the collection and analysis of information to guide police operations, rather than the reverse. 

Power restrictions

In many nations, criminal procedure law has been developed to regulate officers' discretion, so that they do not arbitrarily or unjustly exercise their powers of arrest, search and seizure, and use of force. In the United States, Miranda v. Arizona led to the widespread use of Miranda warnings or constitutional warnings.

In Miranda the court created safeguards against self-incriminating statements made after an arrest. The court held that "The prosecution may not use statements, whether exculpatory or inculpatory, stemming from questioning initiated by law enforcement officers after a person has been taken into custody or otherwise deprived of his freedom of action in any significant way, unless it demonstrates the use of procedural safeguards effective to secure the Fifth Amendment's privilege against self-incrimination" 

Police in the United States are also prohibited from holding criminal suspects for more than a reasonable amount of time (usually 24–48 hours) before arraignment, using torture, abuse or physical threats to extract confessions, using excessive force to effect an arrest, and searching suspects' bodies or their homes without a warrant obtained upon a showing of probable cause. The four exceptions to the constitutional requirement of a search warrant are:
* Consent
* Search incident to arrest
* Motor vehicle searches
* Exigent circumstances

In Terry v. Ohio (1968) the court divided seizure into two parts, the investigatory stop and arrest. The court further held that during an investigatory stop a police officer's search " [is] confined to what [is] minimally necessary to determine whether [a suspect] is armed, and the intrusion, which [is] made for the sole purpose of protecting himself and others nearby, [is] confined to ascertaining the presence of weapons" (U.S. Supreme Court). Before Terry, every police encounter constituted an arrest, giving the police officer the full range of search authority. Search authority during a Terry stop (investigatory stop) is limited to weapons only.

Using deception for confessions is permitted, but not coercion. There are exceptions or exigent circumstances such as an articulated need to disarm a suspect or searching a suspect who has already been arrested (Search Incident to an Arrest). The Posse Comitatus Act severely restricts the use of the military for police activity, giving added importance to police SWAT units.

British police officers are governed by similar rules, such as those introduced to England and Wales under the Police and Criminal Evidence Act 1984 (PACE), but generally have greater powers. They may, for example, legally search any suspect who has been arrested, or their vehicles, home or business premises, without a warrant, and may seize anything they find in a search as evidence.

All police officers in the United Kingdom, whatever their actual rank, are 'constables' in terms of their legal position. This means that a newly appointed constable has the same arrest powers as a Chief Constable or Commissioner. However, certain higher ranks have additional powers to authorize certain aspects of police operations, such as a power to authorize a search of a suspect's house (section 18 PACE in England and Wales) by an officer of the rank of Inspector, or the power to authorize a suspect's detention beyond 24 hours by a Superintendent.

Conduct, accountability and public confidence

Police services commonly include units for investigating crimes committed by the police themselves. These units are typically called Inspectorate-General, or in the US, "internal affairs". In some countries separate organizations outside the police exist for such purposes, such as the British Independent Police Complaints Commission.

Likewise, some state and local jurisdictions, for example, Springfield, Illinois  have similar outside review organizations. The Police Service of Northern Ireland is investigated by the Police Ombudsman for Northern Ireland, an external agency set up as a result of the Patten report into policing the province. In the Republic of Ireland the Garda Síochána is investigated by the Garda Síochána Ombudsman Commission, an independent commission that replaced the Garda Complaints Board in May 2007.

The Special Investigations Unit of Ontario, Canada, is one of only a few civilian agencies around the world responsible for investigating circumstances involving police and civilians that have resulted in a death, serious injury, or allegations of sexual assault. The agency has made allegations of insufficient cooperation from various police services hindering their investigations. 

In Hong Kong, any allegations of corruption within the police will be investigated by the Independent Commission Against Corruption and the Independent Police Complaints Council, two agencies which are independent of the police force.

Due to a long-term decline in public confidence for law enforcement in the United States, body cameras worn by police officers are under consideration. 

Use of force

Police forces also find themselves under criticism for their use of force, particularly deadly force. Specifically, tension increases when a police officer of one ethnic group harms or kills a suspect of another one. In the United States, such events occasionally spark protests and accusations of racism against police and allegations that police departments practice racial profiling.
  
In the United States since the 1960s, concern over such issues has increasingly weighed upon law enforcement agencies, courts and legislatures at every level of government. Incidents such as the 1965 Watts Riots, the videotaped 1991 beating by Los Angeles Police officers of Rodney King, and the riot following their acquittal have been suggested by some people to be evidence that U.S. police are dangerously lacking in appropriate controls.
  
The fact that this trend has occurred contemporaneously with the rise of the US civil rights movement, the "War on Drugs", and a precipitous rise in violent crime from the 1960s to the 1990s has made questions surrounding the role, administration and scope of police authority increasingly complicated.

Police departments and the local governments that oversee them in some jurisdictions have attempted to mitigate some of these issues through community outreach programs and community policing to make the police more accessible to the concerns of local communities, by working to increase hiring diversity, by updating training of police in their responsibilities to the community and under the law, and by increased oversight within the department or by civilian commissions.

In cases in which such measures have been lacking or absent, civil lawsuits have been brought by the United States Department of Justice against local law enforcement agencies, authorized under the 1994 Violent Crime Control and Law Enforcement Act. This has compelled local departments to make organizational changes, enter into consent decree settlements to adopt such measures, and submit to oversight by the Justice Department. 

Protection of individuals

Since 1855, the Supreme Court of the United States has consistently ruled that law enforcement officers have no duty to protect any individual, despite the motto "protect and serve". Their duty is to enforce the law in general. The first such case was in 1855 (') and the most recent in 2005 (Town of Castle Rock v. Gonzales). 

In contrast, the police are entitled to protect private rights in some jurisdictions. To ensure that the police would not interfere in the regular competencies of the courts of law, some police acts require that the police may only interfere in such cases where protection from courts cannot be obtained in time, and where, without interference of the police, the realization of the private right would be impeded.  This would, for example, allow police to establish a restaurant guest's identity and forward it to the innkeeper in a case where the guest cannot pay the bill at nighttime because his wallet had just been stolen from the restaurant table.

In addition, there are Federal law enforcement agencies in the United States whose mission includes providing protection for executives such as the President and accompanying family members, visiting foreign dignitaries, and other high-ranking individuals.  Such agencies include the United States Secret Service and the United States Park Police.

International forces

In many countries, particularly those with a federal system of government, there may be several police or police like organizations, each serving different levels of government and enforcing different subsets of the applicable law. The United States has a highly decentralized and fragmented system of law enforcement, with over 17,000 state and local law enforcement agencies. 

Some countries, such as Chile, Israel, the Philippines, France, Austria, New Zealand and South Africa, use a centralized system of policing.  Other countries have multiple police forces, but for the most part their jurisdictions do not overlap. In the United States however, several different law enforcement agencies may have authority in a particular jurisdiction at the same time, each with their own command.

Other countries where jurisdiction of multiple police agencies overlap, include Guardia Civil and the Policía Nacional in Spain, the Polizia di Stato and Carabinieri in Italy and the Police Nationale and National Gendarmerie in France.

Most countries are members of the International Criminal Police Organization (Interpol), established to detect and fight transnational crime and provide for international co-operation and co-ordination of other police activities, such as notifying relatives of the death of foreign nationals. Interpol does not conduct investigations or arrests by itself, but only serves as a central point for information on crime, suspects and criminals. Political crimes are excluded from its competencies.
INTERPOL International Criminal Police Organisation International Criminal Police Organization International Criminal Police Organization – INTERPOL Interpol (organization) International Police Conference International Police Commission President of Interpol International Criminal Police Organization – Interpol Interpol ICPO-Interpol International Criminal Police Organization - INTERPOL International Criminal Police Commission International Criminal Police Organization - Interpol
international criminal police commission international criminal police organization – interpol international criminal police organization interpol icpo interpol international criminal police organisation interpol organization interpol international criminal police organization international police commission international police conference president of interpol
interpol
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Interpol
 What is the acronym for the agency which provides co- operation between  police forces worldwide? 

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