Common Law and Case Law in the U.S.

Common law and case law form the backbone of American jurisprudence, operating alongside statutory and constitutional sources to shape the rules that govern legal disputes. This page covers how judge-made law develops, how it binds future courts through the doctrine of precedent, and where it fits within the broader sources of U.S. law. Understanding these mechanisms is essential for reading court opinions, anticipating legal outcomes, and grasping why a decision from 1892 can still determine the outcome of a case filed today.

Definition and scope

Common law refers to the body of law derived from judicial decisions rather than from statutes enacted by legislatures or regulations issued by agencies. In the United States, common law descended from the English common law system imported into the colonies before independence, and it continues to develop through the ongoing accumulation of court opinions at both the state and federal levels.

Case law is the broader category: it encompasses every published judicial decision that interprets a statute, applies a constitutional provision, or resolves a dispute without governing legislation. Common law is a subset of case law — specifically, decisions that establish binding rules in areas where no statute governs. The role of precedent and stare decisis formalizes how those decisions bind future courts.

The scope of common law varies significantly by jurisdiction. State courts remain the primary source of common law doctrine in areas such as tort law, contract law, and property law. Federal common law exists but is narrower; the U.S. Supreme Court confirmed in Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), that federal courts sitting in diversity must apply state substantive law rather than a general federal common law, effectively limiting federal judge-made law to specific domains such as admiralty, interstate disputes, and certain constitutional interstices.

How it works

The development of common law follows a structured, iterative process:

Dispute presented — A legal dispute arises that no existing statute fully resolves, or where a statute requires interpretation.
Court issues opinion — A judge or panel of judges issues a written opinion explaining the legal reasoning behind the outcome.
Opinion published — The decision is published in an official reporter (e.g., the United States Reports for Supreme Court decisions, or the Federal Reporter for circuit court decisions compiled by West Publishing).
Precedential weight assigned — Higher court decisions bind lower courts within the same jurisdiction under stare decisis ("to stand by things decided").
Rule abstracted — Subsequent litigants and courts identify the holding — the specific legal rule necessary to decide the case — and distinguish it from dicta, which are observations not necessary to the outcome and not binding.
Rule applied or distinguished — Later courts either follow the precedent, distinguish the facts to reach a different result, or — at the highest level — overrule prior decisions when circumstances warrant.

The U.S. Courts of Appeals produce binding precedent for all district courts within their respective circuits. The Ninth Circuit, for example, covers 9 states and 2 territories, meaning a single panel decision shapes litigation outcomes across that entire geographic footprint. The U.S. Supreme Court issues precedent binding on all federal and state courts when interpreting federal law or the Constitution.

Common scenarios

Common law and case law govern a wide range of disputes. The scenarios below illustrate the functional domains where judge-made rules operate most actively.

Tort liability outside statutory coverage — Negligence doctrine, including the duty-breach-causation-damages framework, is almost entirely common law. No federal statute defines general negligence; instead, courts in each state have built layered doctrine through centuries of opinions. The Restatement (Second) of Torts, published by the American Law Institute (ALI), consolidates these rules but carries persuasive rather than binding authority — courts may adopt or reject its formulations.

Contract disputes with ambiguous terms — When parties dispute what a contract means, courts apply common law rules of interpretation developed through case law: the plain meaning rule, the parol evidence rule, and the contra proferentem doctrine (ambiguities construed against the drafter). The ALI's Restatement (Second) of Contracts and the Uniform Commercial Code (UCC), a model statute adopted in some form by all 50 states, together set the interpretive framework — with UCC Article 2 governing the sale of goods and common law governing service contracts.

Statutory gap-filling — When a federal agency acts under a statute, reviewing courts must determine whether Congress addressed the precise question at issue. Before the Supreme Court's decision in Loper Bright Enterprises v. Raimondo, 603 U.S. ___ (2024), courts applied Chevron deference to agency interpretations of ambiguous statutes (Chevron U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837 (1984)). Loper Bright overruled Chevron, directing courts to exercise independent judgment on statutory meaning — a shift that realigns how case law interacts with administrative law and regulatory agencies.

Constitutional interpretation — The Bill of Rights and the Fourteenth Amendment are enforced almost entirely through case law. Foundational decisions such as Marbury v. Madison, 5 U.S. 137 (1803) (establishing judicial review) and Brown v. Board of Education, 347 U.S. 483 (1954) (interpreting equal protection) illustrate how case law can override prior precedent and reshape statutory and constitutional landscapes. See constitutional law foundations for the structural background.

Decision boundaries

Not every judicial opinion carries the same legal weight. Understanding the classification of judicial decisions is critical for accurate legal research.

Binding vs. persuasive authority

Authority Type	Source	Effect
Binding (mandatory)	Higher court in the same jurisdiction	Must be followed
Persuasive	Courts of equal rank, other jurisdictions, law review articles, Restatements	May be considered but not required

A Ninth Circuit decision on federal statutory interpretation is binding on district courts in California but is only persuasive to courts in the First Circuit. A state supreme court decision on negligence is binding within that state but carries only persuasive weight in other states.

Holdings vs. dicta

The binding element of any case is its holding — the legal principle necessary to resolve the specific facts before the court. Obiter dicta are statements made in passing that were not essential to the judgment. Courts frequently contest whether a particular passage constitutes a holding or dictum, because that characterization determines whether a lower court must follow it.

Distinguishing and overruling

A court that cannot follow a prior case without injustice may distinguish it — arguing the facts differ materially — rather than overruling. Overruling is reserved for the court that originally issued the decision or a superior court. The Supreme Court applies a heightened standard before overruling constitutional precedent, weighing factors including workability, reliance interests, and doctrinal consistency, as articulated in Planned Parenthood of Southeastern Pa. v. Casey, 505 U.S. 833 (1992).

Federal vs. state common law boundaries

Following Erie, state courts resolve questions of state common law independently. A federal court sitting in diversity applies state substantive law but follows federal procedural rules under the Federal Rules of Civil Procedure. This bifurcation means that identical fact patterns can yield different outcomes depending on which court — state or federal — exercises jurisdiction, a dynamic explored in depth under federal vs. state court jurisdiction.

References

Explore This Site

Regulations & Safety Regulatory References Tools & Calculators Court Filing Fee Calculator