The distinctive feature of common law is that it represents the law of the courts as expressed in judicial decisions. The grounds for deciding cases are found in precedents provided by past decisions, as contrasted to the civil law system, which is based on statutes and prescribed texts. Besides the system of judicial precedents, other characteristics of common law are trial by jury and the doctrine of the supremacy of the law. Originally, supremacy of the law meant that not even the king was above the law; today it means that acts of governmental agencies are subject to scrutiny in ordinary legal proceedings.

Judicial precedents derive their force from the doctrine of stare decisis [Lat.,=stand by the decided matter], i.e., that the previous decisions of the highest court in the jurisdiction are binding on all other courts in the jurisdiction. Changing conditions, however, soon make most decisions inapplicable except as a basis for analogy, and a court must therefore often look to the judicial experience of the rest of the English-speaking world. This gives the system flexibility, while general acceptance of certain authoritative materials provides a degree of stability. Nevertheless, in many instances, the courts have failed to keep pace with social developments and it has become necessary to enact statutes to bring about needed changes; indeed, in recent years statutes have superseded much of common law, notably in the fields of commercial, administrative, and criminal law. Typically, however, in statutory interpretation the courts have recourse to the doctrines of common law. Thus increased legislation has limited but has not ended judicial supremacy.

Early common law was somewhat inflexible; it would not adjudicate a case that did not fall precisely under the purview of a particular writ and had an unwieldy set of procedural rules. Except for a few types of lawsuits in which the object was to recover real or personal property, the only remedy provided was money damages; the body of legal principles known as equity evolved partly to overcome these deficiencies. Until comparatively recent times there was a sharp division between common law (or legal jurisprudence) and equity (or equitable jurisprudence). In 1848 the state of New York enacted a code of civil procedure (drafted by David Dudley Field) that merged law and equity into one jurisdiction. Thenceforth, actions at law and suits in equity were to be administered in the same courts and under the same procedure. The Field code reforms were adopted by most states of the United States, by the federal government, and by Great Britain (in the Judicature Act of 1873).