In Erie Railroad Co. v. Tompkins (1938), the U.S. Supreme Court held that a federal court sitting in diversity jurisdiction must apply the substantive law of the state in which it sits — including that state's common law — rather than a body of 'general federal common law.' The decision overruled Swift v. Tyson (1842) and declared, in Justice Brandeis's famous line, that 'there is no federal general common law.' Erie is the case that reoriented the entire relationship between federal and state courts, and it is the doorway into the most heavily tested topic in Civil Procedure.

If you take nothing else away: Erie is not really about a man who lost an arm to a passing train. It is about power — who gets to make the substantive law that decides a state-law claim. The facts are almost incidental. The doctrine is everything.

What is the summary of Erie Railroad Co. v. Tompkins?

Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), was decided by the U.S. Supreme Court in an opinion by Justice Brandeis. Harry Tompkins, a Pennsylvania citizen, was injured by a passing Erie Railroad train while walking along the tracks. He sued the Erie Railroad — a New York corporation — in federal court in New York under diversity jurisdiction. The central question was not whether Tompkins should win, but which body of law the federal court should use to decide whether he could win: Pennsylvania's tort law, or a 'general' federal common law developed by the federal courts themselves. The Supreme Court chose state law, overruled its own 96-year-old precedent, and rewrote the rules of federal diversity litigation.

What are the facts of Erie Railroad v. Tompkins?

Harry Tompkins was walking along a footpath running parallel to the Erie Railroad's tracks in Hughestown, Pennsylvania, at night. A freight train passed, and something — likely an open door on a refrigerator car — struck and knocked him down, and the train severed his arm. Tompkins was a Pennsylvania citizen; the Erie Railroad was incorporated in New York.

The legal significance of the facts turns on a single doctrinal question about duty. Under Pennsylvania common law, a person walking along the tracks was treated as a trespasser, and the railroad owed him no duty except to avoid wanton or willful injury — a standard Tompkins would likely lose under. Under a more general, national tort standard, the railroad might owe him a duty of ordinary care — a standard he could win under. So the outcome of the case depended entirely on which law applied. Tompkins wanted the general federal standard; the railroad wanted Pennsylvania's trespasser rule.

What was the procedural history of Erie v. Tompkins?

Tompkins sued in the U.S. District Court for the Southern District of New York, invoking diversity jurisdiction. The trial court, following Swift v. Tyson, declined to apply Pennsylvania's trespasser rule and instead applied 'general' federal common law of negligence, allowing the jury to find the railroad liable under an ordinary-care standard. Tompkins won a verdict of $30,000. The Second Circuit Court of Appeals affirmed. The Erie Railroad petitioned the Supreme Court, which granted certiorari.

What was the legal issue in Erie Railroad v. Tompkins?

The precise question: When a federal court sits in diversity jurisdiction, must it apply the substantive common law of the state in which it sits, or may it apply a body of 'general federal common law' developed independently by the federal courts under Swift v. Tyson?

Framed at the level your professor cares about: Does the federal government have the power to make substantive common law governing ordinary state-law disputes, or is that power reserved to the states?

What did Erie Railroad v. Tompkins hold?

The Supreme Court held that federal courts sitting in diversity must apply the substantive law of the relevant state — including that state's judge-made common law — and may not substitute a 'general federal common law.' The Court overruled Swift v. Tyson.

The rule of Erie, the part that goes in your outline: Except in matters governed by the federal Constitution or by Acts of Congress, the law to be applied in any case is the law of the state — and there is no federal general common law. In diversity cases, federal courts apply state substantive law. Because Pennsylvania law (through its highest court) governed Tompkins's claim, and Pennsylvania treated him as a trespasser owed only a duty against wanton injury, the case had to be sent back to be decided under that state rule.

What was the reasoning in Erie Railroad v. Tompkins?

Justice Brandeis built the decision on three connected pillars — and you should be able to name all three.

1. Swift v. Tyson misread the Rules of Decision Act. The Rules of Decision Act provides that 'the laws of the several states' shall be the rules of decision in federal court. Swift v. Tyson had read 'laws' to mean only state statutes, not state common law — so federal courts felt free to develop their own general common law. Brandeis, relying in part on research showing the original intent, concluded that 'laws of the several states' includes state common law as declared by the state's highest court. This is the statutory ground.

2. Swift produced injustice and forum shopping. Because federal and state courts could apply different substantive law to the same dispute, outcomes turned on which courthouse you entered. Out-of-state parties could manufacture diversity to escape unfavorable state law, and — as in Black & White Taxicab Co. v. Brown & Yellow Taxicab Co., which Brandeis cited — parties even reincorporated in another state to get into federal court and dodge state law. Swift created 'discrimination by non-citizens against citizens' and made the outcome depend on the accident of diversity. This is the policy ground.

3. The constitutional pillar — the one professors love. Brandeis went further than he needed to. He wrote that Swift was not merely a mistaken statutory interpretation but an unconstitutional assumption of power: 'Congress has no power to declare substantive rules of common law applicable in a state,' and 'no clause in the Constitution purports to confer such a power upon the federal courts.' The federal courts, by inventing general common law, had been exercising a power the Constitution reserves to the states. This constitutional grounding is what makes Erie a landmark and not merely a change of statutory reading — and it is why some scholars argue Erie is best understood as a separation-of-powers / federalism case.

Concurrences and dissent. Justice Reed concurred but resisted the constitutional reasoning — he thought the statutory reading of the Rules of Decision Act was enough and worried about announcing a broad constitutional rule. Justice Butler (joined by McReynolds) dissented, objecting that the Court reached out to decide a huge constitutional question no party had briefed. Know that the constitutional ground was contested even within the majority coalition — that nuance shows up in the sharper cold calls.

Why does Erie Railroad v. Tompkins matter?

Erie is the foundation of the 'Erie doctrine,' one of the two or three most important frameworks in Civil Procedure. Its holding — federal courts in diversity apply state substantive law and federal procedural law — sets up the question that has consumed the courts ever since: where is the line between substance and procedure? Erie tells you to apply state substantive law but leaves the hard cases (statutes of limitations, burden of proof, choice-of-law rules, door-closing statutes) to be worked out later.

Erie sits at the head of a chain of cases your course will march through in order: Guaranty Trust Co. v. York (the 'outcome-determinative' test), Byrd v. Blue Ridge (balancing state interests against federal judicial interests), and Hanna v. Plumer (the modern two-track analysis for whether a Federal Rule applies). You cannot understand any of those without Erie. It is also where the concept of vertical choice of law — federal vs. state — enters the course.

Erie v. Tompkins cold-call prep: the questions your professor will ask

Erie is a cold-call magnet because it rewards students who understand the reasons, not the facts. Expect these:

• "What was the actual question in this case — was it whether Tompkins should recover?" No. The question was which law governs recovery — Pennsylvania's trespasser rule or general federal common law. Don't get baited into arguing the merits of the tort claim.
• "What did Erie overrule, and what was wrong with that case?" Swift v. Tyson (1842). Swift misread 'the laws of the several states' in the Rules of Decision Act to mean only statutes, freeing federal courts to make general common law. That produced forum shopping and unequal treatment of litigants.
• "Give me all three grounds for the decision." (1) Statutory: the Rules of Decision Act includes state common law. (2) Policy: Swift caused forum shopping and discrimination. (3) Constitutional: neither Congress nor the federal courts have power to make general substantive common law. If you only give the statutory ground, you've missed the point of the case.
• "Why did the Court reach the constitutional question if the statutory reading resolved it?" This is the trap-door question. The honest answer: it didn't strictly need to, which is exactly why Justice Reed concurred and Justice Butler dissented. Brandeis wanted to bury Swift permanently and root the rule in federalism so a future Congress couldn't revive general federal common law. Naming Reed's concurrence here scores points.
• "Does Erie mean federal courts always apply state law?" No — only substantive law, and only where the Constitution or an Act of Congress doesn't govern. Federal courts still apply federal procedural law. That distinction is the whole ballgame for the next three weeks.
• "Whose interpretation of Pennsylvania law controls?" The Pennsylvania Supreme Court's — the state's highest court. Federal courts must follow the state's own declaration of its common law, not their own view of what the law 'should' be.

How does Erie show up on the exam?

Erie itself is rarely the whole answer on an exam — it's the gateway. The classic issue-spotter gives you a diversity case where a state rule and a federal practice (or Federal Rule) conflict: a state statute of limitations vs. a federal filing rule, a state rule on expert affidavits, a state door-closing statute. Your job is to run the Erie analysis.

The trap 1Ls fall into: stopping at Erie and saying 'apply state law because it's diversity.' That's wrong and incomplete. Erie is step one. The real analysis asks: Is there a conflict between state law and a federal rule? If a valid Federal Rule of Civil Procedure is on point, you run Hanna v. Plumer and the Rules Enabling Act, not raw Erie. If there's no Federal Rule directly on point, you run the Guaranty Trust outcome-determinative test as refined by Byrd and Hanna's 'twin aims' (discouraging forum shopping and avoiding inequitable administration of the law). The strong answer names Erie, then immediately shows which track the conflict falls on. Citing Erie's twin policy aims — anti-forum-shopping and equal treatment — is what separates an A from a B.

The other exam move: knowing that Erie applies to state common law, not just statutes, and that federal courts in diversity must use the forum state's choice-of-law rules (that last point comes from Klaxon v. Stentor, often taught right after Erie).

What cases are taught alongside Erie Railroad v. Tompkins?

• Swift v. Tyson (1842) — the case Erie overruled; the source of 'general federal common law.'
• Guaranty Trust Co. v. York (1945) — introduced the 'outcome-determinative' test for substance vs. procedure.
• Byrd v. Blue Ridge Rural Electric Cooperative (1958) — added a balancing of state and federal judicial interests.
• Hanna v. Plumer (1965) — the modern framework; when a Federal Rule of Civil Procedure is on point, it governs if valid under the Rules Enabling Act.
• Klaxon Co. v. Stentor Electric (1941) — federal diversity courts apply the forum state's choice-of-law rules.

Learn these as a single arc. Erie states the principle; the others tell you how to apply it when state and federal rules collide.