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 Idaho, as in other states, common law plays a significant role in the legal system. It is the body of law that emerges from court decisions when judges resolve lawsuits. When Idaho's state legislature has not enacted a statute addressing a particular legal issue, courts rely on common law principles to decide cases. These principles are derived from judicial precedent, meaning that Idaho courts look to how similar cases have been decided in the past. Under the doctrine of stare decisis, Idaho courts are generally bound to follow the decisions of higher courts within the same jurisdiction, such as the Idaho Supreme Court or the U.S. Supreme Court, when those decisions are relevant to a case at hand. However, when an Idaho court faces a legal question that has not been previously addressed by statute or case law within its jurisdiction—a situation known as a matter of first impression—the court will attempt to resolve the issue by drawing analogies to similar laws and applying concepts of fairness and justice.