Erie Doctrine Explained for Law Students

The Erie doctrine, from Erie Railroad Co. v. Tompkins (1938), establishes that federal courts sitting in diversity must apply state substantive law and federal procedural law. Before Erie, federal courts applied a general federal common law that often differed from state law, leading to forum shopping. Erie eliminated this by requiring federal courts to follow the state's substantive rules.

When a plaintiff from New York sues a defendant from California in federal court (diversity jurisdiction), which state's laws apply? Erie provides the framework:

Substantive questions (elements of a tort claim, contract interpretation, damages caps) → Apply state law
Procedural questions (rules of evidence presentation, pleading requirements, discovery procedures) → Apply federal law (Federal Rules of Civil Procedure)

When there's a conflict between federal and state law, apply this analysis:

Step 1: Is there a Federal Rule of Civil Procedure (FRCP) on point?
If yes → Apply the FRCP if it's valid under the Rules Enabling Act (it usually is). See Hanna v. Plumer.

Step 2: Is there a federal statute on point?
If yes → Apply the federal statute if it's constitutional (it almost always is).

Step 3: If no FRCP or statute, is it a judge-made federal practice?
Apply the Erie/Guaranty Trust outcome-determinative test: Would applying the federal practice lead to forum shopping or inequitable administration of the law? If yes → apply state law.

The hardest part of Erie is distinguishing substance from procedure. Some rules are clearly substantive (statutes of limitations, elements of claims). Some are clearly procedural (pleading format, discovery rules). But many fall in a gray area:

Statute of limitations: Substantive (apply state law) — Guaranty Trust v. York
Burden of proof: Substantive (apply state law)
Service of process: Procedural (apply FRCP) — Hanna v. Plumer
Attorney-client privilege: In diversity cases, apply state law under FRE 501

Erie questions almost always appear on Civ Pro exams. The key is to follow the framework methodically:

1. Identify the conflict between federal and state rules
2. Determine if there's an FRCP, federal statute, or judge-made practice involved
3. Apply the appropriate test
4. Reach a conclusion

Don't skip steps. Professors want to see you work through the analysis, even if the answer seems obvious.