Walbrun v. Babbitt was a United States Supreme Court case that dealt with the issue of whether a patent for a machine was valid. The plaintiff, Walbrun, had invented a machine for cutting and shaping wood, and had applied for a patent for it. The defendant, Babbitt, had then made a similar machine and was selling it. Walbrun sued Babbitt for patent infringement. The Supreme Court held that Walbrun's patent was valid, and that Babbitt had infringed upon it. The Court found that Walbrun's invention was novel and useful, and that it was not obvious to someone skilled in the art. The Court also found that Walbrun had adequately described the invention in his patent application, and that Babbitt had copied it. The Court's decision established that a patent is valid if it meets the requirements of novelty, usefulness, and non-obviousness, and that a patent holder can sue for infringement if someone else copies their invention. This case is still cited today as an important precedent in patent law.

In Walbrun v. Babbitt, the Supreme Court was asked to decide whether a patent for an invention could be issued when it had already been used by another person prior to its application. The majority opinion held that since the invention had already been put into use, no patent should be granted and thus affirmed the decision of the lower court denying Walbrun's claim. In dissent, Justice Field argued that while he agreed with much of what his colleagues said in their opinion, he believed there were certain circumstances where a patent could still be validly issued even if someone else had previously used it before applying for one themselves. He reasoned that as long as they were not aware of any other person using or claiming rights over their invention at the time they applied for a patent then they should still have some protection under law from those who would try to take advantage of them afterwards. Furthermore, Field noted that Congress intended patents to encourage inventors and promote progress in science and useful arts which would not happen if people were denied patents simply because someone else happened upon their idea first without ever filing an application themselves