Park ‘N Fly, Inc. (PNF) (plaintiff) owned and operated airport parking lots. PNF obtained a service mark for “Park ‘N Fly” in 1971. Approximately six years later, PNF filed a proper affidavit and obtained incontestable status from the U.S. Patent and Trademark Office (PTO) for the mark. Dollar Park and Fly, Inc. (Dollar Park) (defendant) operated a similar airport parking lot business. In 1978, PNF brought suit against Dollar Park for service mark infringement. Dollar Park filed a counterclaim, seeking to cancel PNF’s registration for “Park ‘N Fly.” Dollar Park defended the infringement claim on the grounds that PNF’s mark was merely descriptive. The United States District Court for the District of Oregon granted PNF an injunction. The court of appeals reversed. The United States Supreme Court granted certiorari.