Common law is the body of legal rules built from written court decisions rather than from statutes passed by a legislature. When judges resolve disputes, they issue opinions explaining their reasoning, and those opinions become binding guides for how similar disputes must be handled in the future. This judge-made law forms the backbone of the legal systems in the United States, the United Kingdom, Canada, Australia, and dozens of other countries whose courts trace their traditions to England. Where no statute speaks to a situation, common law fills the gap by drawing on centuries of accumulated judicial reasoning.
How Common Law Differs From Civil Law
The world’s legal systems generally fall into one of two families. In a common law system, the law develops case by case. Judges examine the facts, look at how similar disputes were resolved before, and issue written opinions that carry binding authority over future cases. The law is largely uncodified. Statutes exist, but judges interpret them, and those interpretations carry as much practical weight as the statutes themselves.
Civil law systems work differently. Countries like France, Germany, Japan, and most of Latin America rely on comprehensive written codes that attempt to spell out the rule for every category of dispute. Judges apply the code to the facts, but their individual decisions do not bind future cases the same way. The code is the law; the judge administers it. Common law systems, by contrast, treat judges as active participants in shaping the law itself.
The common law tradition spread globally through British colonization. The United States, Canada, Australia, India, and many countries in Africa and the Caribbean operate under some form of it. Several countries blend both traditions, but the core distinction holds: in common law systems, past court decisions are a primary source of legal authority, not merely illustrations of how a written code should be applied.
How Judicial Precedent Works
Precedent is the engine that drives common law forward. When a judge issues a written opinion, the legal reasoning in that opinion becomes a reference point for every future case raising the same issue within that jurisdiction. Court opinions are collected and published in volumes called case reporters, and even though most research now happens online, the reporter system remains the organizing framework for how cases are cited and found.1Northern Illinois University. Case Law Reporters – Basic Legal Research
Not every word in a judicial opinion carries the same weight. The binding part of a decision is the holding: the specific legal conclusion the court reached to resolve the dispute in front of it. If you could remove a statement from the opinion and the outcome would stay the same, that statement is dicta, Latin for something said in passing. Dicta can influence future courts and signal where the law may be heading, but no lower court is required to follow it. Lawyers spend considerable energy arguing about where that line falls, because reclassifying a prior court’s statement as dicta rather than holding can change the outcome of a case entirely.
Binding vs. Persuasive Precedent
Precedent comes in two varieties, and the difference has real consequences. Binding precedent means a lower court must follow the ruling of a higher court within the same jurisdiction. A federal district court in Chicago is bound by decisions of the Seventh Circuit Court of Appeals, and both are bound by the U.S. Supreme Court. A judge who personally disagrees with a binding precedent still has to apply it. That constraint is the point: it keeps the law consistent regardless of which judge happens to hear your case.
Persuasive precedent comes from courts outside a judge’s chain of command. A ruling from a California appellate court has no binding authority on a court in New York, but a New York judge might find the California reasoning compelling and choose to adopt it. Trial court decisions, even within the same jurisdiction, are generally persuasive only, since they sit at the bottom of the judicial hierarchy.1Northern Illinois University. Case Law Reporters – Basic Legal Research Courts facing an issue for the first time often look to persuasive precedent from other states to fill the void.
Stare Decisis: Why Courts Follow Past Decisions
The formal name for the obligation to follow precedent is stare decisis, a Latin phrase meaning “let the decision stand.” The principle exists because a legal system where outcomes shift with every new judge would be useless for planning. Businesses sign contracts, property owners invest in improvements, and individuals structure their affairs based on how courts have ruled before. Stare decisis protects those expectations by requiring courts to apply established rules to similar facts.2United States Court of Appeals for the Armed Forces. Miscellaneous Matters – Judicial Review – Stare Decisis
The doctrine also constrains judicial power. Federal judges are not elected, and even elected state judges serve long terms. Stare decisis prevents any single judge from rewriting the law based on personal philosophy. The collective judgment of generations of courts, refined case by case, carries more authority than any individual’s view of what the law should be.
Stare decisis is powerful but not absolute. Courts occasionally overrule their own prior decisions, though the party asking for that outcome carries a heavy burden. The U.S. Supreme Court weighs factors like whether the earlier decision was well-reasoned, whether the rule has proven workable, whether later cases have eroded its logic, whether the factual assumptions still hold, and whether people have structured their affairs around it in ways that make overruling it genuinely disruptive.3Constitution Annotated. ArtIII.S1.7.2.3 Stare Decisis Factors Reliance interests often prove decisive. Even when a majority of justices believe a prior case was wrongly decided, the disruption of overruling it can outweigh the benefit of getting the law “right.”
Courts are especially reluctant to overturn precedent that interprets a statute, because the legislature can always amend the statute if it disagrees with how courts read it. Constitutional precedent gets somewhat less protection, since amending the Constitution is far harder.3Constitution Annotated. ArtIII.S1.7.2.3 Stare Decisis Factors
Where the Common Law Came From
The common law traces back to England after the Norman Conquest in 1066. Before the conquest, disputes were handled locally, with each region applying its own customs. The Norman kings established royal courts and sent judges on circuit across the countryside to resolve disputes under a unified body of law. That law became “common” precisely because it applied to everyone in the realm, replacing the patchwork of local rules.4H2O. The Development of the Common Law
Over centuries, English courts built an enormous body of case law covering property, contracts, inheritance, and personal wrongs. English colonists brought this tradition to North America. After independence, most states formally adopted English common law through reception statutes, legislative acts that incorporated the existing body of English case law as the baseline for the new state’s legal system. Even today, courts occasionally trace a legal principle back to an English decision from the 1600s or 1700s when no American case squarely addresses a question.
Where Common Law Still Governs Today
Several major fields of law remain dominated by common law principles even where legislatures have layered statutes on top. The relationship between judge-made rules and statutory additions varies by area, but in each, the common law foundation still drives how disputes get resolved.
Tort Law
Tort law governs civil wrongs like negligence, trespass, and defamation. The core question in most tort cases, whether someone failed to exercise reasonable care, is a standard courts developed over centuries of deciding individual disputes. Legislatures have passed statutes addressing specific safety obligations, damage caps, and procedural requirements, but the underlying framework remains judicial. When a court decides whether a doctor was negligent or a property owner should have fixed a broken stairway, it is applying principles that descend directly from English case law.
Contract Law
The basic elements of a valid contract (offer, acceptance, and something of value exchanged between the parties) were defined by courts, not legislatures. Statutes like the Statute of Frauds add requirements for specific types of agreements, such as mandating that contracts for the sale of land be in writing.5Legal Information Institute. Statute of Frauds But the vast body of rules governing how contracts are formed, interpreted, breached, and enforced remains rooted in judicial decisions.
Property Law
Property disputes regularly turn on common law doctrines that have existed for centuries. Adverse possession, which allows someone to gain legal ownership of land by openly occupying it for a statutory period, originated in common law courts. So did the law of easements, which governs rights to use another person’s land for specific purposes like access roads or utility lines. Legislatures have modified some of these rules, but the underlying concepts remain products of judicial development.
Employment at Will
The default employment relationship in the United States is a common law creation. Under the at-will doctrine, either the employer or the employee can end the relationship at any time, for any reason that is not illegal, or for no reason at all. Every state except Montana presumes employment is at will unless a written contract says otherwise.6Bureau of Labor Statistics. The Employment-at-Will Doctrine – Three Major Exceptions
Courts have carved out three exceptions. The public-policy exception protects employees fired for things like reporting illegal activity or refusing to break the law. The implied-contract exception applies when an employer’s handbook or oral promises create a reasonable expectation of job security without a formal written agreement. A smaller number of states recognize a covenant of good faith, which prohibits terminations motivated by bad faith or malice, such as firing someone right before their pension vests.6Bureau of Labor Statistics. The Employment-at-Will Doctrine – Three Major Exceptions All three were developed by judges, not legislatures.
Criminal Law Is the Exception
One area where common law has lost almost all of its former territory is criminal law. Historically, crimes were defined by judges. The Enlightenment-era push toward democratic governance changed this, on the principle that only elected legislatures should have the power to declare something a crime and attach penalties to it. Today, most states have abolished common law crimes by statute, meaning you can only be prosecuted for conduct a legislature has specifically defined as illegal. A few states still technically recognize common law offenses through reception statutes, but prosecutions under those provisions are extremely rare because comprehensive criminal codes now cover virtually every situation those old rules once addressed.
When Statutes Override Common Law
Common law is never the final word on any legal question. When a legislature passes a statute that conflicts with an existing common law rule, the statute wins. Legislatures can correct judicial rulings they disagree with, fill gaps in case law, or modernize rules that developed under very different social conditions. This power ensures that elected officials have the last word on major policy questions.
Sometimes legislatures codify an entire area of law, gathering scattered common law principles into a single written code. The Uniform Commercial Code is the most prominent example in the United States. Commercial transactions were historically governed by a sprawling body of case law that varied from state to state. The UCC organized those rules into a standardized set of statutes that every state has adopted, giving businesses confidence that the same rules apply whether they are operating in Maine or Montana.7Uniform Law Commission. Uniform Commercial Code
Even after codification, common law doesn’t disappear. Judges still interpret statutory language, and when a statute is ambiguous, courts frequently look to the common law background to figure out what the legislature meant.
Common Law Marriage Is a Narrow Exception
When people hear “common law,” many immediately think of common law marriage, and the topic generates more confusion than almost any other area. A common law marriage is a legally recognized marriage that forms without a license or ceremony when a couple meets specific requirements: living together, presenting themselves to the public as married, and intending to be married.
Only a handful of jurisdictions currently allow new common law marriages to form. As of 2026, those jurisdictions are Colorado, Iowa, Kansas, Montana, Rhode Island, Texas, Utah, and the District of Columbia.8National Conference of State Legislatures. Common Law Marriage by State New Hampshire recognizes common law marriage only for inheritance purposes. Several other states, including Georgia, Ohio, Oklahoma, and Pennsylvania, recognize common law marriages created before a specific cutoff date but no longer allow new ones.
The most important thing to understand is that if you have a common law marriage, you need a real divorce to end it. The marriage does not dissolve just because the couple separates or stops living together. Without a formal divorce, you remain legally married, which affects your ability to remarry, your tax filing status, your liability for a spouse’s debts, and your rights to property division and spousal support.
Federal Courts and State Common Law
A persistent source of confusion in American law is the relationship between federal courts and state common law. The short version: there is no general federal common law. When a federal court hears a case because the parties are from different states (known as diversity jurisdiction), it must apply the substantive law of the state where the dispute arose, including that state’s common law. The federal court uses federal procedural rules, but the principles governing who wins and loses come from state law.
This rule comes from the 1938 Supreme Court decision in Erie Railroad Co. v. Tompkins, which held that federal courts must treat state common law as binding state law, not as something federal judges are free to disregard or replace. The goal is to prevent a litigant from getting a different legal outcome simply by filing in federal court instead of state court.
Federal common law does still exist in a few narrow areas where the federal government has a unique interest. Admiralty and maritime law is the clearest example; courts apply a body of federal common law to disputes arising on navigable waters, and Congress may revise those rules by statute.9Constitution Annotated. ArtIII.S2.C1.12.1 Overview of Admiralty and Maritime Jurisdiction Disputes between states and certain matters involving the rights and obligations of the federal government also fall under federal common law. For the vast majority of civil litigation in federal courts, though, state common law controls the outcome.