Common law is law that develops through court decisions rather than through legislation. When a court resolves a dispute, it states a rule that later courts follow in similar cases. Over time those rulings accumulate into a body of law that governs contracts, torts, property, and many other areas. The United States inherited the common law tradition from England, and it remains the foundation of most American state legal systems.
Where Common Law Comes From
After the Norman Conquest, English royal courts began recording decisions and applying them consistently across the kingdom. That shared body of judge-made rules became known as the common law, meaning law common to the whole realm rather than local custom. When American states formed, they generally adopted the common law as it existed at the time, either by constitutional provision, statute, or court decision. Louisiana is the best-known exception, because its legal system draws heavily on the civil law tradition of France and Spain.
Stare Decisis
The engine of common law is stare decisis, a Latin phrase meaning to stand by things decided. A court must generally follow the holding of a higher court in the same jurisdiction, and courts usually respect their own prior decisions. A decision that binds later courts is called precedent. Not every statement in an opinion is binding; only the holding, the part of the reasoning necessary to decide the case, carries that weight. Other statements are dicta, which may be persuasive but are not controlling.
Stare decisis promotes stability and predictability. It also lets the law evolve. A court can distinguish a prior case whose facts differ, and a higher court can overrule a precedent when it concludes the earlier decision was wrong or no longer workable.
Common Law, Statutory Law, and Equity
| Source | Who creates it | Example |
|---|---|---|
| Common law | Courts, through decisions | Negligence, contracts, property rules |
| Statutory law | Legislatures | Tax codes, traffic laws, criminal statutes |
| Regulatory law | Agencies | Rules issued under delegated authority |
| Equity | Courts, historically separate | Injunctions, specific performance |
Statutes now cover many areas once governed by common law, and a statute can change or replace a common law rule. Courts still interpret those statutes, so common law reasoning remains relevant even where legislation is the primary source. Equity developed alongside the common law to provide remedies that money damages could not, such as an injunction. In most American jurisdictions law and equity are now administered in the same courts, but the distinction still matters in some procedures.
Common Law in the Federal System
There is no general federal common law. In Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), the Supreme Court held that federal courts exercising diversity jurisdiction must apply state substantive law, including state common law, rather than a judge-made federal rule. Federal common law survives only in limited areas where federal interests are strong, such as certain disputes over federal property or interstate water rights. This is why a federal court hearing a state-law claim looks to the decisions of that state's courts.
How Common Law Grows
Common law develops case by case. A court decides the dispute before it, states a rule, and applies it. Later courts treat that rule as binding or persuasive, refine it, or limit it. Restatements published by the American Law Institute collect and organize these rules, and courts often cite them as persuasive authority even though they are not law. Legal treatises and law review articles can also influence how courts frame an issue.
Common Law and Statutory Interpretation
When a statute uses a term that has an established common law meaning, courts often presume the legislature intended that meaning unless the statute says otherwise. Courts also apply the rule that statutes in derogation of the common law are construed narrowly. These presumptions connect the two sources of law and show why old decisions can still shape the reading of a modern statute.
Other Meanings of Common Law
The term has a second, narrower sense in family law. A common law marriage is a marriage formed without a license or ceremony when the parties meet certain requirements, such as living together and holding themselves out as married. Only a minority of states recognize common law marriage, and the requirements differ. This is a different concept from the common law tradition, though the name is the same.
Common Law and Civil Law Systems
Common law is one of the world's major legal traditions, and civil law is another. In a civil law system, courts rely primarily on comprehensive codes and give less weight to individual decisions. Judges in that tradition often have a more investigative role. Common law systems, by contrast, build rules from decided cases and treat precedent as a primary source. Many countries blend the two, and even in the United States, code-based areas such as tax and bankruptcy coexist with common law areas such as torts and contracts.
Why Common Law Still Matters
Even when a statute governs a topic, courts must interpret its words, and they often draw on common law principles to do so. Common law rules also fill gaps where no statute applies, which is common in contracts, property, and torts. Understanding the common law helps a reader predict how a court might resolve a dispute and why a lawyer cites old decisions alongside new statutes. It also explains the structure of many legal doctrines that appear in everyday cases.
Where to Learn More
Cornell's Legal Information Institute at law.cornell.edu offers free explanations of common law, precedent, and the Erie doctrine. Federal and state court opinions are published on court websites, and many are available through the Government Publishing Office at govinfo.gov. The American Law Institute publishes the Restatements, which many law libraries and court websites describe. Because common law is jurisdiction-specific, the decisions of the relevant state's courts are the controlling authority.
This guide is general legal information, not legal advice. How common law applies to a particular dispute depends on the jurisdiction and the facts, so consult a licensed attorney for advice.
Common Law vs. Civil Law Systems
Common law is one of the two dominant legal traditions. In a common law system, such as the United States, England, and most former British colonies, judges decide individual cases and those decisions guide later courts through precedent. In a civil law system, used in much of continental Europe, Latin America, and parts of Asia, legislatures enact comprehensive codes and judges apply them, with less weight given to prior decisions. The difference shapes how lawyers research, how courts reason, and how quickly the law can change. Even within the United States, Louisiana blends civil law traditions because of its French and Spanish history.