St. Paul Plough Works v. Starling was a United States Supreme Court case that addressed the issue of whether a patentee could recover damages for infringement of a patent that had been declared invalid. The plaintiff, St. Paul Plough Works, had obtained a patent for a plough, which was later declared invalid by the Circuit Court of the United States for the District of Minnesota. The defendant, Starling, had infringed on the patent by manufacturing and selling a similar plough. The Supreme Court held that the patentee could not recover damages for infringement of a patent that had been declared invalid. The Court reasoned that the patentee had no right to the exclusive use of the invention, and thus could not recover damages for infringement. The Court also noted that the patentee had not been deprived of any property rights, as the patent had been declared invalid before the infringement occurred. The Court concluded that the patentee could not recover damages for infringement of a patent that had been declared invalid. The Court reasoned that the patentee had no right to the exclusive use of the invention, and thus could not recover damages for infringement. The Court also noted that the patentee had not been deprived of any property rights, as the patent had been declared invalid before the infringement occurred.

In St. Paul Plough Works v. Starling, the Supreme Court was tasked with determining whether a patent for an improved plow could be enforced against someone who had purchased and used parts of the patented invention from another source without authorization from the patent holder. The majority opinion held that such use constituted infringement on the patent rights of the inventor, but Justice Field dissented in his opinion arguing that since no part of any infringing device was made by or under authority of its owner, there could not have been any infringement upon the plaintiff's rights as set forth in their patent. He further argued that it would be unjust to punish those who innocently purchase and use components which are found to infringe upon a validly issued patent when they were unaware at time of purchase that such components violated said patents' terms and conditions.