Illinois Tool Works Inc. (Illinois Tools) (defendant) owned a company that manufactured a printing system consisting of patented inkjet printheads and ink containers, as well as unpatented ink. Illinois Tools sold printers to manufacturers, who received a license from Illinois Tool to utilize the patented components of the system. As a condition of purchasing the system, the manufacturers agreed to buy all their ink needs from Illinois Tool. Independent Ink, Inc. (Independent Ink) (plaintiff), began selling ink products identical to the ink offered by Illinois Tool. Illinois Tool brought an infringement action, but the action was dismissed. Independent Ink then brought a suit against Illinois Tool, claiming that Illinois Tool’s business model was an unlawful tying arrangement in violation of antitrust law. The district court granted Illinois Tool’s motion for summary judgment. The court of appeals reversed, finding that a patent owner was presumed to have market power in a tying product and that engaging in a tying arrangement with market power was a per se violation of antitrust law. Illinois Tool appealed the decision.