---
title: "Erie Doctrine"
type: Legal Rule
source: https://casebriefly.com/legal-rules/erie-doctrine
---

# Erie Doctrine

The Erie doctrine requires federal courts sitting in diversity to apply state substantive law and federal procedural law, preventing forum shopping and inequitable administration of the law between federal and state courts in the same state.

## Definition

The Erie doctrine, established in Erie Railroad Co. v. Tompkins (1938), holds that there is no general federal common law and that federal courts exercising diversity jurisdiction must apply the substantive law of the state in which they sit, including state common law as declared by state courts. This landmark decision overruled Swift v. Tyson (1842), which had allowed federal courts to develop their own general common law independent of state courts, leading to forum shopping and the inequitable administration of justice.

The central challenge under Erie is distinguishing substance from procedure. The Supreme Court has developed several analytical frameworks for this determination. The outcome-determinative test from Guaranty Trust Co. v. York (1945) asks whether applying federal law rather than state law would significantly affect the outcome of litigation. The Byrd balancing test from Byrd v. Blue Ridge Rural Electric Cooperative (1958) weighs the state interest in the rule against the federal interest in maintaining the essential characteristics of the federal system. The Hanna framework, from Hanna v. Plumer (1965), provides the most important analytical structure, distinguishing between Federal Rules of Civil Procedure and judge-made federal practices.

Under Hanna, if a Federal Rule of Civil Procedure or federal statute directly conflicts with a state rule, the Federal Rule applies if it is valid under the Rules Enabling Act (it must not abridge, enlarge, or modify any substantive right). If no Federal Rule is on point and the conflict is with a judge-made federal practice, courts apply the twin aims of Erie: whether applying the federal practice would encourage forum shopping or lead to inequitable administration of the law.

## Elements

- Federal courts in diversity must apply state substantive law
- Federal courts apply federal procedural law
- If a Federal Rule directly conflicts with state law, apply the Federal Rule if valid under the Rules Enabling Act
- If no Federal Rule is on point, apply the twin aims of Erie: avoiding forum shopping and inequitable administration of the law
- State law includes not only statutes but also state common law as declared by the state's highest court

## Key Case

Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938)

## Landmark Cases

| Name | Citation | Significance |
| --- | --- | --- |
| Erie Railroad Co. v. Tompkins | 304 U.S. 64 (1938) | Overruled Swift v. Tyson and held that federal courts in diversity must apply state substantive law, eliminating the concept of general federal common law. |
| Guaranty Trust Co. v. York | 326 U.S. 99 (1945) | Introduced the outcome-determinative test: if applying the federal rule would significantly affect the outcome, the state rule is substantive and must be applied. |
| Byrd v. Blue Ridge Rural Electric Cooperative, Inc. | 356 U.S. 525 (1958) | Added a balancing test weighing the state interest in the rule against the federal interest in maintaining the character of the federal system. |
| Hanna v. Plumer | 380 U.S. 460 (1965) | Created the modern Erie framework distinguishing between direct conflicts with Federal Rules (apply the Rule if REA-valid) and unguided Erie choices (apply the twin aims). |
| Shady Grove Orthopedic Associates, P.A. v. Allstate Insurance Co. | 559 U.S. 393 (2010) | Applied the Hanna framework and held that FRCP Rule 23 governed class certification even where state law prohibited class actions for certain claims. |

## Exam Tips

- Start every Erie analysis by asking: Is there a Federal Rule of Civil Procedure or federal statute directly on point? If yes, apply Hanna step one (REA validity). If no, apply the twin aims of Erie.
- The substance/procedure distinction is the heart of Erie. Always frame the issue in terms of the specific conflict between the state and federal rules, not in the abstract.
- Remember that Erie applies only in diversity jurisdiction. In federal question cases, federal courts may develop and apply federal common law.
- Watch for statutes of limitations, burden of proof, and choice-of-law rules, which are typically characterized as substantive under Erie.

## Common Mistakes

- Applying the outcome-determinative test in isolation; it was supplemented by Byrd and largely subsumed into the Hanna framework.
- Failing to identify the threshold question of whether a Federal Rule directly conflicts with the state rule, which determines whether the Hanna or twin aims analysis applies.
- Assuming Erie applies to federal question cases; it applies only when federal courts exercise diversity or supplemental jurisdiction over state-law claims.

## Mnemonic Or Memory Aid

Erie two tracks: (1) Federal Rule on point? REA valid? Apply it. (2) No Rule? Twin aims: no forum shopping, no inequity.

## Related Rules

- diversity-jurisdiction
- subject-matter-jurisdiction
- federal-question-jurisdiction

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Source: [Erie Doctrine — CaseBriefly](https://casebriefly.com/legal-rules/erie-doctrine)