In a prior infringement action, a patent held by the University of Illinois Foundation (Foundation) (plaintiff) was determined to be invalid. Thereafter, the Foundation brought this action against Blonder-Tongue Laboratories (Blonder-Tongue) (defendant) in the district court for alleged infringement of the same patent. The Foundation was allowed to maintain this infringement action against Blonder-Tongue in the district court, and the Foundation prevailed at trial. The court of appeals affirmed the district court’s judgment in favor of the Foundation. Blonder-Tongue appealed to the United States Supreme Court, arguing that nonmutual collateral estoppel precluded the Foundation’s maintenance of this subsequent infringement action because the patent’s invalidity was established in the earlier action.