Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), was a landmark U.S. Supreme Court decision in which the Court held that there is no general American federal common law and that U.S. federal courts must apply state law, not federal law, to lawsuits between parties from different states that do not involve federal questions. In reaching this holding, the Court overturned almost a century of federal civil procedure case law, and established the foundation of what remains the modern law of diversity jurisdiction as it applies to United States federal courts.