Case law or common law is the law made by courts. It is known as case law because it derives from judicial decisions in legal cases rather than from written statutes. This means that as a court decides and reports its decision concerning a particular suit, this case becomes part of the body of law and can be consulted in later cases involving similar problems.

Prior to the development of constitutional and statutory law, controversies were decided on the basis of established customs. If there were no established customs, judges decided a case on the basis of what they considered to be right and wrong. As these decisions began to be recorded, judges were directed to look for guidance to the decision in a prior case that had similar facts. This use of precedents is known as stare decisis — literally, “to stand by (previous) decisions.” Stare decisis is important because it provides for consistency in the application of common law and offers some assurance to a person seeking relief in the courts as to the rules governing the likely outcome of the case.

Cases are published in reporters (such as United States Reports) that are produced either by the government or a private publishing firm. Not all cases are published.