In Erie Railroad Co v Tompkins, 304 U.S. 64 (1938), the U.S. Supreme Court held that federal district courts in diversity jurisdiction cases must apply the law of the states in which they sit, including the judicial doctrine of the state’s highest court, where it does not conflict with federal law. In so ruling, it overturned nearly 100 years of precedent created under Swift v. Tyson, 41 U.S. 1 (1842).
