S1
S1, S01, S.I, S-1, S.1, Š-1 or S 1 may refer to:

Biology and chemistry
 S1 nuclease, an enzyme that digests singled-stranded DNA and RNA
 S1: Keep locked up, a safety phrase in chemistry
 Primary somatosensory cortex, also known as S1
 Tegafur/gimeracil/oteracil, also known as S-1, a chemotherapy medication

Entertainment
 S1 (Indian TV channel), a Hindi-language channel
 S1 (Swiss TV channel), a German-language channel
 S1 (producer), a hip hop producer, member of the group Strange Fruit Project
 S1 No. 1 Style, a Japanese adult video company
 Gibson S-1, a guitar made by the Gibson Guitar Corporation
 A member of the S1W (group) that later became part of the music group Public Enemy.

Government
 Bill S-1, a pro forma bill in Canadian Parliament
 Form S-1, a U.S. Securities and Exchange Commission filing
 S-1 Executive Committee, a United States government entity during World War II 
 S1 (military), an administrative position within military units

Technology
 ACPI S1 power state in computing
 Apple S1, integrated computer used in the Apple Watch
 Canon PowerShot S1 IS, a 2004 3.2 megapixel digital camera
 FinePix S1 Pro, a 2000 interchangeable lens digital single-lens reflex camera by Fujifilm
 Nikon Coolpix S1, a digital camera
 S1 Corporation, an American software development company
 S1 Core, a microprocessor-core
 S1 MP3 Player
 Samsung Galaxy S also commonly called S1 is a smartphone from 2010
 Sendo S1, a Sendo mobile phone model
 Siemens S1, a Siemens mobile phone
 Sony BDP-S1, a first generation Blu-ray Disc (BD) Player
 S1, an EPC in an LTE/4G network

Transportation

Routes

China
 Line S1 (Beijing Subway)
 Line S1 (Nanjing Metro)
 Line S1 (Wenzhou Rail Transit)
 S1 Yingbin Expressway in Shanghai

Germany
 S1 (Berlin), an S-Bahn line
 S1 (Dresden), an S-Bahn line
 S1 (Munich), an S-Bahn line
 S1 (Nuremberg), an S-Bahn line
 S1 (Rhine-Main S-Bahn), an S-Bahn line
 S1 (Rhine-Ruhr S-Bahn), an S-Bahn line
 S1 (Stuttgart), an S-Bahn line
 a planned Bremen S-Bahn line
 a Hamburg S-Bahn line
 a Hanover S-Bahn line
 a RheinNeckar S-Bahn line
 a Rostock S-Bahn line
 a Stadtbahn Karlsruhe line

Switzerland
 S1 (RER Vaud), an S-Bahn line
 S1 (St. Gallen S-Bahn), an S-Bahn line
 S1 (ZVV), now subsumed by S24, a Zürich S-Bahn line

United States
 County Route S1 (California)
 S1 (Long Island bus)

Other countries
 S1 (Vienna), an S-Bahn line in Austria
 Line S1 (Milan suburban railway service), Italy
 S1 National Highway, a National Highways of Pakistan
 Expressway S1 (Poland)
 FGC line S1, a suburban train line in Barcelona Province, Spain
 Stagecoach Gold bus route S1, in Oxfordshire, England, UK

Vehicles

Aircraft
 Blackburn Buccaneer S.1 jet naval strike aircraft
 Focke-Wulf S 1, a German Focke-Wulf aircraft
 Fokker S.I, a 1919 Dutch primary trainer aircraft
 Hopfner S-1, a Hopfner aircraft
 Letov S-1, a 1920 Czechoslovak surveillance aircraft
 Loening S-1, a United States Army Air Service seaplane
 Loughead S-1 Sport 1920 US biplane
 Martinsyde S.1, a 1914 British biplane aircraft
 Pantsir-S1, a Russian anti-aircraft system
 Pitts S-1 aerobatic biplane
 S-1 Loening, a United States Army Air Service seaplane
 SSBS S1, a French experimental rocket
 Swift S-1, a 1991 Polish single seat aerobatic glider

Cars
 Audi S1, performance variant of Audi A1
 Invicta S1, a 2004 sports car
 S1 Scout Car, an armoured car built in Australia during the Second World War
 Superformance S1 Roadster, a Lotus Seven Type replicar produced in South Africa 2001–2004

Other vehicles
 Alco S-1, a locomotive
 PRR S1, a duplex locomotive developed by the Pennsylvania Railroad
 USS S-1 (SS-105), a 1918 United States Navy experimental submarine

Other uses
 S1 (classification), a disability swimming classification
 S postcode area covering Sheffield City Centre
 in human anatomy:
 the first sacral vertebra
 the sacral spinal nerve 1 of the vertebral column
 the primary somatosensory cortex in the brain
 Senior 1, the First Year in the Scottish secondary education system
 Season (television) or series one
 Comet Ikeya-Seki, C/1965 S1
 Upplands regemente (signal), a 1902 Signal Regiment of the Swedish Armed Forces

With superscripts and subscripts
S1 may refer to :
 S1 (heart sound), a heart sound in cardiac auscultation
S1 may refer to :
 S1, the n-sphere in two dimensions i.e. a circle
 Inverse second (s−1), a unit of frequency

S01
S01 may refer to :
 Akai S01, an Akai synthesizer
 ATC code S01 Ophthalmologicals, a subgroup of the Anatomical Therapeutic Chemical Classification System
 HMS Porpoise (S01), a 1956 Porpoise-class submarine of the Royal Navy
 MULTI-S01, an encryption algorithm based on a pseudorandom number generator