Charles Berlitz (defendant) authored a series of “Passport” language books containing his name and a disclaimer on the book cover. The disclaimer was required to dispel any misconception that Charles Berlitz was connected with the Berlitz Schools of Languages of America (Berlitz Schools) (plaintiff). In a prior action, Berlitz Schools sued Charles Berlitz in New York state court for unfair competition and trademark dilution, challenging the sufficiency of the disclaimer. The state court held that the disclaimer sufficed to dispel confusion. That judgment was affirmed on appeal. Thereafter, Charles Berlitz authored a new “Step-by-Step” series of language books. His name and the same disclaimer appeared on the cover, though in different proportions. Berlitz Schools brought this action for trademark infringement and unfair competition against Charles Berlitz in the United States District Court for the Southern District of New York. Charles Berlitz moved for summary judgment on the grounds that the doctrine of collateral estoppel precluded Berlitz Schools from relitigating the sufficiency of the disclaimer. The district court granted Charles Berlitz’s motion for summary judgment. Berlitz Schools appealed, arguing that differences in the facts precluded the application of collateral estoppel.