While walking along the railroad tracks, Harry Tompkins (plaintiff), a citizen of Pennsylvania, was injured by a train owned by Erie Railroad Co. (Erie) (defendant). Tompkins sued Erie, a New York company, for negligence in New York federal court. At trial, Erie argued that Tompkins was a trespasser and, under Pennsylvania state law, the company was not liable unless its conduct was wantonly negligent. Tompkins argued that federal general law should apply and determine Erie’s duty and liability. The trial judge applied the rule from Swift v. Tyson, 41 U.S. (16 Pet.) 1 (1842), holding that federal courts were only bound to apply state statutory and customary law, not state common law. Thus, the trial court applied the general law. Because the majority rule was that railroad company owed a duty of ordinary care to travelers like Tompkins, the district court granted recovery for Tompkins. The circuit court affirmed judgment for Tompkins claiming that federal courts could use their discretion on matters of general law. The United States Supreme Court granted certiorari.