Case law is the law developed through the courts over time, based upon precedent. It is also referred to as common law and is distinguished from statutes, treaties, administrative law, etc. Case law is based on legal principles developed in earlier case law, instead of statutory laws. It is the traditional law of an area or region created by judges when deciding individual disputes or cases. Case law changes over time.
The U.S. is a common law country. In all states except Louisiana, which is based on Napoleonic code, the common law of England was adopted as the general law of the state, or varied by statute. Today almost all case law has been enacted into statutes with modern variations by all the states.