Yale Lock Manufacturing Company v. Sargent was a United States Supreme Court case in which the Court held that a patentee may not use a patent to prevent others from making a product that is not covered by the patent. The case involved a dispute between Yale Lock Manufacturing Company and Sargent & Company over the use of a patented lock. Yale Lock Manufacturing Company had patented a lock that was used to secure doors and windows. Sargent & Company had developed a similar lock, but it was not covered by the patent. Yale Lock Manufacturing Company sued Sargent & Company for patent infringement, arguing that Sargent & Company's lock was an infringement of its patent. The Supreme Court disagreed, holding that a patentee may not use a patent to prevent others from making a product that is not covered by the patent. The Court reasoned that a patentee should not be able to use a patent to prevent competition in the market. The Court's decision in Yale Lock Manufacturing Company v. Sargent established an important principle in patent law: a patentee may not use a patent to prevent others from making a product that is not covered by the patent. This principle has been applied in numerous cases since then, and it has been an important factor in protecting competition in the market.

In the case of Yale Lock Manufacturing Company v. Sargent, the Supreme Court was tasked with determining whether a patent for an improved lock mechanism held by Yale Lock Manufacturing Company (Yale) had been infringed upon by Sargent. The majority opinion found that there had not been infringement and thus dismissed the complaint brought against Sargent. In his dissenting opinion, Justice Field argued that while it may be true that some elements of Yale's patented invention were not present in Sargent's product, those elements were merely improvements on existing technology and did not constitute essential features of the invention as a whole. He further noted that even if these improvements could be considered essential to the invention, they were still present in some form within Sargents' product and therefore constituted infringement under patent law. As such, he concluded that justice would have been better served if judgment had gone in favor of Yale instead of being dismissed entirely