Mimmack v. United States was a United States Supreme Court case that dealt with the issue of whether a patentee could assign a patent to a third party without the consent of the United States. The case involved a patentee, Mimmack, who had assigned a patent to a third party without the consent of the United States. The United States argued that the assignment was invalid because it had not been approved by the United States. The Supreme Court held that the assignment was valid and that the United States had no right to interfere with the assignment. The Court reasoned that the patentee had the right to assign the patent to a third party without the consent of the United States. The Court further held that the United States could not interfere with the assignment because it had no right to do so. In conclusion, the Supreme Court held that the assignment of the patent to a third party was valid and that the United States had no right to interfere with the assignment. The Court reasoned that the patentee had the right to assign the patent to a third party without the consent of the United States.

Justice Field delivered the dissenting opinion in Mimmack v. United States, arguing that Congress had no authority to pass a law allowing for the forfeiture of property without due process of law. He argued that such an act was unconstitutional and violated the Fifth Amendment's guarantee against deprivation of life, liberty or property without due process. Furthermore, he noted that while it may be true that forfeitures are sometimes necessary to protect public interests, they should only be allowed when there is sufficient evidence presented before a court to prove guilt beyond a reasonable doubt. In this case, however, no such proof existed as all parties involved were acquitted by jury trial and thus could not have their rights taken away through forfeiture proceedings alone. As such Justice Field concluded his dissent by stating "the power claimed by Congress cannot exist under our Constitution."