Pfaff (plaintiff) sued Wells (defendant) for infringing a patent claiming a type of computer component. Pfaff had been contracted by Texas Instruments to develop the component in November 1980, and he presented sketches of his concept in March 1981. On April 8, 1981, Pfaff entered into a written agreement to sell the product to Texas Instruments, more than one year prior to his April 19, 1982 filing date, having never made a prototype of the invention. After entering into the agreement, Pfaff sent the designs to a manufacturer to mass produce the invention, though the manufacturer was forced to create new machinery to make the device. The manufacturer managed to make the first component in the summer of 1981, less than one year prior to Pfaff’s filing date. Pfaff eventually learned of Wells’ manufacturing of an accused device, and he filed suit. The district court held that, because the reduction to practice occurred less than a year before the filing date, Pfaff was entitled to patent protection. Under the district court’s reasoning, an offer for sale under 35 U.S.C. §102(b) could not take place if the invention being offered was not reduced to practice. The court of appeals reversed on the basis of the offer for sale more than one year prior to the filing date, and due to the fact that the invention was “substantially complete” when the offer for sale was made. Pfaff petitioned for a writ of certiorari, which was granted.