Erie doctrine

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United States federal civil procedure doctrines
Justiciability
Advisory opinions Standing Ripeness Mootness Political questions Constitutional avoidance
Jurisdiction
Subject-matter Federal question Diversity Amount in controversy Supplemental Removal Class Action Fairness Act of 2005 Personal In personam In rem Quasi in rem
Federalism
Erie doctrine Abstention Anti-Injunction Act Sovereign immunity Abrogation Rooker–Feldman doctrine Adequate and independent state ground
v t e

The Erie doctrine is a fundamental legal doctrine of civil procedure in the United States which mandates that a federal court called upon to resolve a dispute not directly implicating a federal question (most commonly when sitting in diversity jurisdiction, but also when applying supplemental jurisdiction to claims factually related to a federal question or in an adversary proceeding in bankruptcy) must apply state substantive law.

The doctrine follows from the Supreme Court landmark decision in Erie Railroad Co. v. Tompkins (1938). The case overturned Swift v. Tyson, which allowed federal judges sitting in a state to ignore the common law local decisions of state courts in the same state in diversity actions.