Common law is the system of deciding cases that originated in England and which was latter adopted in the U.S. Common law is based on precedent (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. Common 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 common law has been enacted into statutes with modern variations by all the states. Broad areas of the law, such as property, contracts and torts are traditionally part of the common law. Because these areas of the law are mostly within the jurisdiction of the states, state courts are the main source of common law. The area of federal common law is primarily limited to federal issues that have not been addressed by a statute.