Wollensak v. Reiher was a United States Supreme Court case that dealt with the issue of whether a patentee could sue for infringement of a patent after the patent had expired. The plaintiff, Wollensak, had obtained a patent for a machine for making paper bags. After the patent expired, Reiher began making and selling a similar machine. Wollensak sued Reiher for patent infringement. The Supreme Court held that a patentee could not sue for infringement of a patent after the patent had expired. The Court reasoned that the patentee had already received the benefit of the patent, which was the exclusive right to make, use, and sell the invention for the duration of the patent. Once the patent expired, the patentee no longer had any exclusive rights and could not sue for infringement. The Court also noted that allowing a patentee to sue for infringement after the patent had expired would be unfair to the infringer, who would be liable for damages even though the patentee had already received the benefit of the patent. In conclusion, the Supreme Court held that a patentee could not sue for infringement of a patent after the patent had expired. The Court reasoned that the patentee had already received the benefit of the patent and that allowing a patentee to sue for infringement after the patent had expired would be unfair to the infringer.

In Wollensak v. Reiher, the United States Supreme Court was tasked with determining whether a patent for an invention of a machine used to make paper bags could be granted when it had been previously denied by the Patent Office. The majority opinion held that since there were prior patents issued for similar machines and because this particular invention did not have any new features or improvements over those already patented, no patent should be granted. Justice Field dissented from this decision arguing that although there may have been some similarities between the two inventions, they were still distinct enough to warrant granting a separate patent as long as all other requirements of novelty and utility were met. He argued that if inventors are discouraged from making minor changes in existing designs then progress would suffer greatly due to lack of innovation and creativity in developing new products or improving upon old ones.