Common law is a legal system in which courts develop the rules of law through written decisions in individual cases, with later courts generally bound to follow those earlier rulings. It grew out of medieval England, where traveling judges resolved disputes using local customs and shared principles of fairness, then recorded their rulings so similar cases could be decided the same way across the kingdom. Today it is the foundation of the legal systems in the United States, the United Kingdom, Canada, Australia, and dozens of other countries shaped by English legal tradition.
The practical consequence is simple. Much of the law that governs your daily life — what counts as negligence, how a contract gets enforced, what a landlord owes a tenant — was not written by a legislature. It was built, decision by decision, by judges resolving real disputes.
How Precedent Works
The engine of common law is a principle called stare decisis, Latin for “stand by things decided.” When an appellate court rules on a legal question, that decision binds every lower court in the same jurisdiction. A later judge facing similar facts has to follow the earlier ruling and reach a consistent result. That is what gives common law its predictability: you can look at how courts have handled situations like yours and form a reasonable expectation of the outcome.
Binding authority flows downward through the court hierarchy. A state supreme court’s reading of a contract rule controls how every trial court in that state treats the same issue. Courts also look at persuasive authority — decisions from courts in other states, or from lower courts, that carry no binding force but offer useful analysis. A judge handling a novel insurance dispute may study how a court in another state resolved a similar question, even though that ruling does not formally control the outcome.
When Courts Depart From Precedent
Stare decisis is strong, but it is not absolute. Higher courts can overrule their own earlier decisions when the circumstances justify the change. The U.S. Supreme Court has identified several factors it weighs before departing from an established ruling:1Justia U.S. Supreme Court. Janus v. AFSCME, 585 U.S. ___ (2018)
- Quality of the original reasoning
- Workability of the rule in practice
- Consistency with the court’s later decisions
- Whether society’s understanding of the underlying facts has shifted
- How heavily people, businesses, and institutions have relied on the prior rule
Overruling is treated as a serious step. Simple disagreement with an earlier decision is generally not enough. Courts weigh the cost of unsettling expectations against the benefit of correcting a rule they now believe is wrong.
Judge-Made Law and Statutory Interpretation
Not every situation has a statute covering it. When a dispute arises in an area the legislature has not addressed, common law judges resolve it by drawing on established customs, logical reasoning, and principles from past decisions. The court’s written opinion then creates a new rule — the product sometimes called judge-made law.
A case with no prior court decision on the legal question is called a case of first impression. With no binding precedent to follow, the judge reasons from scratch, drawing on persuasive authority from other jurisdictions, scholarly commentary, and general legal principles. That new ruling becomes the starting point for future courts facing the same issue. Judges also turn to the Restatements of the Law, published by the American Law Institute, which summarize how courts around the country have handled specific topics like contracts, torts, and property. Restatements have no force of law on their own, but courts rely on them regularly as a framework for analysis.
This gap-filling role is what lets common law adapt. As technology produces disputes no legislature anticipated, from data privacy to autonomous vehicles to digital assets, courts can develop rules in real time rather than waiting for new legislation.
Even where a statute does exist, its text is often broad or ambiguous. A law might require “reasonable care” or prohibit “unfair business practices” without defining those terms for every scenario. Common law courts resolve the ambiguity by interpreting the statute in the context of actual cases. A court might consider a distracted-driving law and decide whether it covers holding a paper map, not just a phone. Once a court issues a formal interpretation, that reading becomes part of the law surrounding the original text, and future courts look to it. In practice, the law governing any particular situation is a combination of the statute’s words and the accumulated judicial explanations of how those words apply.
Money Damages and Equitable Remedies
Early common law courts could generally award only one kind of remedy: money. That worked for many disputes, but in some situations no dollar amount could fix the problem. If you needed to stop a neighbor from tearing down a historic building, or force a seller to go through with a contract for a unique piece of land, a payment alone solved nothing.
Equity developed as a parallel set of remedies to fill that gap. Under equitable principles, courts can order specific performance, requiring someone to do exactly what they promised, or issue an injunction prohibiting a harmful action. Equity focuses on the overall fairness of the situation rather than applying rules mechanically. A judge may consider whether a party acted in good faith or tried to exploit a technicality to gain an unfair advantage.
Historically, separate courts handled legal claims (for money) and equitable claims (for injunctions and performance orders). The United States ended that divide with the Federal Rules of Civil Procedure in 1938, which merged law and equity into a single form of civil action.2Cornell Law School. U.S. Constitution Annotated – Cases Combining Law and Equity Today, a single court can award money damages, order specific performance, issue an injunction, or combine remedies depending on what the situation requires.
Common Law vs. Civil Law
Most countries follow one of two broad legal traditions: common law or civil law. The difference comes down to where the law primarily lives and who drives the process.
In a common law system, judicial precedent is central. Courts build the law case by case, and past decisions bind future courts. The process is adversarial. Two opposing parties present their arguments to a judge, and often a jury, who acts as a neutral referee. Lawyers for each side control the investigation, gather the evidence, and make the case. The judge moderates the proceeding and, in a jury trial, determines the legal consequences after the jury decides the facts.
In a civil law system, used across much of continental Europe, Latin America, and parts of Asia and Africa, the law is organized into comprehensive written codes. Judges apply those codes to disputes. Past decisions may carry some influence, but they do not formally bind future courts the way common law precedent does. The judge takes a more active role in investigating facts, questioning witnesses, and directing the proceedings rather than refereeing between adversaries.
Many legal systems blend elements of both. South Africa and the Philippines combine civil law codes with common law principles. Louisiana is a hybrid within the United States: its private law follows a civil code tradition, while criminal and commercial matters run on common law principles.
Where Common Law Applies Today
Common law remains the primary legal framework across a significant portion of the world, largely because of England’s influence during centuries of colonization and trade. The United Kingdom still operates under common law, and the system took root in nearly every territory where English governance was established.
In the United States, common law governs legal interactions in all fifty states. The significant exception is Louisiana, which inherited its private-law tradition from France and Spain. Louisiana adopted its first civil code in 1808, modeled heavily on the French tradition, and still uses a civil code for areas like property, family law, and contracts.3U.S. District Court for the Eastern District of Louisiana. An Introduction to Louisiana’s Civil Law Tradition For criminal law, constitutional questions, and commercial matters governed by uniform national codes, Louisiana functions much like the rest of the country.
Canada’s legal landscape is similarly split. Every province and territory except Quebec uses common law. Quebec maintains a civil code rooted in its French colonial heritage.4Department of Justice Canada. Canada’s System of Justice Australia, India, and many other former British colonies also rely on common law as their foundation, though each jurisdiction has layered its own statutes and constitutional framework on top of the shared tradition.
A Note on “Common Law Marriage”
The phrase “common law” also appears in a completely different context: common law marriage. Despite the shared name, that term refers to a specific type of marital relationship — a legally recognized union between two people who never obtained a marriage license or held a ceremony, formed instead through mutual agreement, cohabitation, and holding themselves out publicly as married. Only about ten states and the District of Columbia currently allow new common law marriages to be formed. If you landed here looking for information on that topic, it is a separate subject from the broader legal system described above.