Civil Procedure
Erie Doctrine
Definition
The Erie doctrine, established in Erie Railroad Co. v. Tompkins, requires federal courts sitting in diversity to apply state substantive law and federal procedural law. This landmark decision overruled Swift v. Tyson and eliminated the notion of federal general common law. Determining whether a rule is substantive or procedural involves the outcome-determinative test (Guaranty Trust), the Byrd balancing test, and the Hanna analysis for Federal Rules of Civil Procedure (asking whether a valid federal rule directly conflicts with the state rule).
Example
A federal court in diversity applies federal rules of evidence (procedural) but must apply the state's statute of limitations and choice-of-law rules (substantive).