Common law—also known as case law, court opinions, judicial precedent, or judge-made law—is the body of law within each state or federal circuit that is created when judges write decisions (court opinions) resolving lawsuits—and in doing so sometimes apply legal principles that are not included in the state or federal statutes. When the state legislature or the U.S. Congress has not passed a law (state or federal statute) governing a certain legal issue, the courts look to traditional (and sometimes new) legal principles to resolve those issues. And those principles—as stated in case law—are the common law.

The concept of common law is derived from the English system and is based on precedent—the manner in which courts have previously resolved a similar legal dispute involving similar factual circumstances. If a similar legal dispute involving similar facts has been resolved in a certain way in the past, a current court is generally required to follow the prior application of the law under the doctrine of stare decisis—a Latin term pronounced “starry duh-sigh-suss”—to maintain consistency and predictability in the law. But a court’s obligation to follow precedent is generally limited to case law from higher courts (generally the state supreme court or the U.S. Supreme Court) or from the same court (district court of appeals or federal circuit court, for example).

And if a court determines a dispute involves a legal issue that is not addressed in a statute or in a previous court opinion from the same state or jurisdiction (and thus is a matter of first impression) the court will resolve the dispute as best it can—often by analogy to similar statutes and legal principles—as well as the more subjective ideas of fairness and justice.

In California, common law refers to the body of law that is created by judges through their written decisions in court cases. This occurs when there is no specific statute governing a particular legal issue, and judges must rely on legal principles from past cases, known as precedents, to resolve disputes. The doctrine of stare decisis requires California courts to follow the legal principles established in higher court decisions, such as those from the California Supreme Court or the U.S. Supreme Court, to ensure consistency and predictability in the law. When a case presents a new issue that has not been previously decided (a matter of first impression), California courts will attempt to resolve the issue by drawing analogies to similar statutes and legal principles, while also considering concepts of fairness and justice. This system allows the law to evolve and adapt over time as new types of disputes arise.