Common law
The common lawso named because it was "common" to all the king's courts across Englandoriginated in the practices of the courts of the English kings in the centuries following the Norman Conquest in 1066. Prior to the Norman Conquest, much of England's legal business took place in the local folk courts of its various shires and hundreds. A variety of other individual courts also existed across the land: urban boroughs and merchant fairs held their own courts, as did the universities of Oxford and Cambridge, and large landholders also held their own manorial and seigniorial courts as needed. Additionally, the Catholic Church operated its own court system that adjudicated issues of canon law.
Common law
For example, in most U.S. states, the criminal statutes are primarily codification of pre-existing common law. (Codification is the process of enacting a statute that collects and restates pre-existing law in a single document—when that pre-existing law is common law, the common law remains relevant to the interpretation of these statutes.) In reliance on this assumption, modern statutes often leave a number of terms and fine distinctions unstated—for example, a statute might be very brief, leaving the precise definition of terms unstated, under the assumption that these fine distinctions will be inherited from pre-existing common law. (For this reason, many modern American law schools teach the common law of crime as it stood in England in 1789, because that centuries-old English common law is a necessary foundation to interpreting modern criminal statutes.)