State vs Federal Case Law: Which One Governs Your Case

State case law interprets a state's own constitution, statutes, and common law and binds only the courts of that state. Federal case law interprets the U.S. Constitution and federal statutes and binds federal courts, with the U.S. Supreme Court binding everyone. Most everyday disputes, contracts, property, torts, family law, and the bulk of criminal prosecution, are governed by state case law, not federal.

Which body of law governs is the first question in any research project, and getting it wrong costs you the afternoon. You can find a beautifully on-point case, read it carefully, build an argument around it, and discover it carries no weight at all in the court you are standing in. This guide covers how to tell which system controls, how the two cross over, and what to do when the authority you found is from the wrong one.

What is the difference between state and federal case law?

The difference is which sovereign's law the court is interpreting, and which courts have to listen.

State case law is the accumulated body of published opinions from a state's appellate courts, interpreting that state's constitution, its statutes, and its common law. A decision of the Supreme Court of California binds every court in California and no court anywhere else. State courts handle the overwhelming majority of American litigation: something on the order of ninety-five percent of cases filed in the United States are filed in state courts.

Federal case law is the body of published opinions from the federal courts, interpreting the U.S. Constitution, federal statutes, and federal common law. It is organized in a hierarchy: district courts at the trial level, thirteen circuit courts of appeals above them, and the U.S. Supreme Court at the top. A circuit's published decision binds the district courts within that circuit and nobody else. A U.S. Supreme Court decision on a question of federal law binds every court in the country, state and federal alike.

Which court's decisions bind mine?

Work up your own hierarchy, and stop when you leave it. The rule of thumb that survives contact with almost every situation:

• A court is bound by the courts above it in its own system. A California superior court is bound by the California Courts of Appeal and the Supreme Court of California.
• A court is not bound by courts in a parallel system. A California state judge is not bound by the Ninth Circuit on a question of California law, however persuasive the reasoning.
• Everyone is bound by the U.S. Supreme Court on federal questions. That is the one line that runs through both systems.
• Everything else is persuasive. Useful, citable, sometimes decisive when nothing better exists, but never controlling.

The state court structures themselves vary more than people expect, which is why the hierarchy question is genuinely worth checking rather than assuming. Texas has two courts of last resort, one for civil matters and one for criminal. In New York the Supreme Court is the trial court and the Court of Appeals is the top court, the reverse of the usual naming. In Florida and California, an intermediate appellate decision can bind trial courts across the entire state, not just in its own district. We break down each of these in our case law search by state guides.

When does a federal court apply state case law?

Constantly, and this is the crossover that catches people out. Under the Erie doctrine, from Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), a federal court hearing a state-law claim under diversity jurisdiction must apply the substantive law of the state, including that state's case law. There is no general federal common law for these questions.

So a federal judge in Houston deciding a Texas breach of contract claim applies Texas contract law, and the Supreme Court of Texas is the final authority on what that law means. If the Texas high court has spoken, the federal judge follows it, full stop. If it has not, the federal court makes an "Erie guess" about how the state's highest court would rule, usually leaning on the state's intermediate appellate decisions.

The practical upshot for research: being in federal court does not mean you research federal case law. If your claim arises under state law, you research state case law, and you research it in the state whose law governs, which the choice-of-law analysis decides and which is not always the state you are sitting in.

When does a state court apply federal case law?

Whenever a federal question arises, which happens more often than the clean separation suggests. State courts routinely decide federal constitutional issues: a suppression motion under the Fourth Amendment in a state criminal case, a First Amendment defense in a state tort suit, a federal preemption argument against a state statute. State courts have concurrent jurisdiction over most federal claims.

Here the hierarchy has an asymmetry worth knowing. On a federal question, a state court is bound by the U.S. Supreme Court. It is not bound by the federal circuit court that sits over its geography. A Georgia state court deciding a federal constitutional question is not obliged to follow the Eleventh Circuit; that decision is persuasive authority. State supreme courts have on occasion disagreed with their local circuit on a point of federal law, and the disagreement stands until the U.S. Supreme Court resolves it.

Can I cite a case from another state?

You can, and it is persuasive authority only. It never binds. Out-of-state authority is genuinely valuable in a few situations: when your state has no case on the question, when the other state's statute uses the same language as yours (especially with a uniform act like the UCC), or when the decision comes from a court whose reasoning is widely respected on that subject, such as Delaware on corporate governance.

Two rules make this work. Be candid about what it is: tell the court plainly that the authority is persuasive rather than controlling, because a judge who discovers you implied otherwise will discount everything else in the brief. And check whether your own courts have already rejected that approach, since a foreign case your state has explicitly declined to follow is worse than no case at all.

How do I know which law governs my case?

Ask three questions in order.

What is the claim? Breach of contract, negligence, adverse possession, divorce, most criminal charges: state law. Federal statutory claims (Title VII, the ADA, securities, patent, bankruptcy), constitutional claims against government actors, and disputes governed by federal statute: federal law. If your answer lands on the federal side, our guide to federal case law search covers the circuit hierarchy and where the opinions live.

Which court are you in, and why? Federal court on a state-law claim through diversity still applies state substantive law under Erie. State court on a federal claim still applies federal law. The forum and the governing law are separate questions, and conflating them is the single most common research error.

Which state's law? If there is a choice-of-law clause, start there. If not, the forum's conflict-of-laws rules decide, and the answer may point at a state you have never practiced in.

Once you have the governing law, find the highest on-point authority inside that hierarchy, then work outward to persuasive authority only if nothing on point exists. That workflow, from issue to verified citation, is laid out in how to research case law, and the mechanics of binding versus persuasive weight are covered in binding vs persuasive precedent.

Doing the search itself

Once you know which hierarchy governs, the search is a matter of finding the on-point case inside it and confirming it still stands. Free sources will retrieve an opinion you already know about: the state judiciary websites, Google Scholar, and CourtListener all carry appellate opinions at no cost. What they do not do well is surface the case you have never heard of, because keyword search rewards whoever guesses the words the court happened to use, and they do not tell you whether a case is still good law. Confirming that last part is a citator job, and it is the step that most often gets skipped.

That is the gap Cases is built for. You describe the issue in plain English, pick the jurisdiction, and get on-point precedents back as headnote cards with a plain-English summary, the holding, and a real citation you confirm in the official reporter. It searches U.S. federal and state case law, and it shows you the citation precisely so you stay the one who verifies it.

Cases is informational research, not legal advice. Whatever you use to find a case, read the opinion, confirm the citation at the source, and check that it is still good law before you rely on it.