That which derives its force and authority from the universal consent and immemorial practice of the people. The system of jurisprudence that originated in England and which was latter adopted in the U.S. that is based on precedent instead of statutory laws.
Traditional law of an area or region; also known as case law. The law created by judges when deciding individual disputes or cases. The body of law which includes both the unwritten law of England and the statutes passed before the settlement of the United States.
In Old England there were two types of Courts - law and equity. In the law court the Judge applied statutes. As time went on situations that were not covered by statutes were uncovered and Judges 'created' law, usually in equity. This is 'common law.'
The U.S. is a common law country. In all states except Louisiana (which is based on the French civil code), the common law of England was adopted as the general law of the state, EXCEPT when a statute provides otherwise. Common law has no statutory basis; judges establish common law through written opinions that are binding on future decisions of lower courts in the same jurisdiction. Broad areas of the law, most notably relating to property, contracts and torts are traditionally part of the common law. These areas of the law are mostly within the jurisdiction of the states and thus state courts are the primary source of common law. Thus, 'common law' is used to fill in gaps. Common law changes over time, and at this time, each state has its own common law on many topics. The area of federal common law is primarily limited to federal issues that have not been addressed by a statute.
Even if federal common law otherwise would operate, it is displaced when Congress has decided the matter. See, e.g., Central Bank v. First Interstate Bank of Denver, N.A., 114 S.Ct. 1439, 1448 (1994) (holding that the conclusion that Congress did not intend to impose aiding and abetting liability under section 10(b) of the Securities and Exchange Act 'resolve[d] the case' notwithstanding the acknowledged power of the federal courts, with respect to the section 10(b) actions, to fashion federal common law that 'attempt[s] to infer `how . . . Congress would have addressed the issue,'' (quoting Musick, Peeler & Garrett v. Employers Ins. of Wausau, 113 S.Ct. 2085, 2090 (1993).