In Illinois, a railway train owned by Illinois Terminal Railroad (the railroad) (defendant) struck a vehicle driven by Margaret O’Leary (plaintiff). Margaret’s minor daughter, Judith (plaintiff), was injured in the collision. The O’Learys were residents of Missouri. The O’Learys filed a negligence suit in Missouri state court against the railroad. The railroad raised the affirmative defense of contributory negligence. The O’Learys requested the trial court to instruct the jury according to Missouri’s law on contributory negligence, which required the railroad to prove that Margaret was contributorily negligent in causing the collision. The trial court applied Missouri law and awarded the O’Learys $7,000 in damages. The railroad appealed, arguing that the trial court erred in instructing the jury according to Missouri law. Instead, the railroad claimed that the trial court should have applied Illinois law, which would require the O’Learys to show that Margaret acted with ordinary care. The court of appeals disagreed and affirmed the judgment of the trial court. On its own motion, the court of appeals transferred the matter to the Supreme Court of Missouri for review.