Davis v. Gray is a landmark United States Supreme Court case that established the principle of federal preemption in the area of patent law. The case involved a dispute between two inventors, Charles Davis and William Gray, over the patent rights to a machine for printing bank notes. Davis had obtained a patent for the machine from the United States Patent Office, while Gray had obtained a patent from the state of Massachusetts. The Supreme Court held that the federal patent granted to Davis preempted the state patent granted to Gray, and thus Davis was the rightful owner of the patent. The Court reasoned that the federal patent system was established to promote the progress of science and the useful arts, and that the federal government had exclusive authority to grant patents. The Court further held that the federal patent system preempted any state patent system, and thus the federal patent granted to Davis was superior to the state patent granted to Gray. This decision established the principle of federal preemption in the area of patent law, and has been cited in numerous subsequent cases.

In Davis v. Gray, the Supreme Court was tasked with deciding whether a state law that granted exclusive rights to an individual to operate a business in violation of the Fourteenth Amendment's Equal Protection Clause could be enforced. The majority opinion held that such laws were unconstitutional and thus unenforceable. Justice Field dissented from this decision, arguing that while he agreed with the majority’s conclusion regarding equal protection under the Constitution, he believed it was beyond Congress' power to invalidate state legislation on these grounds. He argued further that if Congress had such authority then it would have been given explicitly by either Article I or Article IV of the Constitution; since no explicit grant exists, states should retain their right to pass laws as they see fit without interference from Congress or federal courts. In addition, Field noted his belief that any attempt by Congress or federal courts to interfere in matters traditionally left up for determination by states would lead only to confusion and conflict between different jurisdictions within our nation's legal system