Pfaff v. Wells Electronics, Inc., 525 U.S. 55 (1998), was a decision by the Supreme Court of the United States that determined what constituted being "on sale" for the purposes of barring the grant of a patent for an invention. Background of the case In November 1980, the plaintiff, engineer Wayne Pfaff, was asked by Texas Instruments to design for them a socket for the mounting and removal of semiconductor chip carriers. Pfaff proceeded to draw designs for the socket, which he showed to Texas Instruments in March 1981. On April 8, 1981, Texas Instruments provided a written purchase order to buy over 30,000 of the sockets. The sockets were not actually built, however, until July 1981. Pfaff applied for a patent for the socket on April 19, 1982, and received the patent in 1985. He then proceeded to sue the defendant, Wells Electronics, Inc., for patent infringement when Wells made a socket that was too similar to Pfaff's design. Wells, in defense, claimed that Pfaff's patent was invalid. In support of this assertion, Wells pointed to 35 U.S.C. § 102(b), which states that an inventor shall not be entitled to a patent if: ...the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country, more than one year prior to the date of the application for patent in the US. Wells asserted that by accepting the purchase order from Texas Instruments, Pfaff had placed the invention "on sale" one year and one week before applying for the patent, which would make it invalid under § 102(b). Pfaff countered that the invention had not been reduced to practice, meaning that a working model had not yet been made. Pfaff's contention was that the invention was not complete at the time of the purchase order, and therefore could not have been "on sale" yet. The District Court for the Northern District of Texas upheld Pfaff's patent, but the Court of Appeals for the Federal Circuit reversed, finding the patent invalid because the invention was "substantially complete" at the time of the sale. Pfaff then appealed to the Supreme Court. Issue The Supreme Court noted that lower courts had offered different opinions on the question of whether an invention could be "on sale" within the meaning of the statute before it had actually reduced to practice. The