Kelley v. Milan was a United States Supreme Court case that addressed the issue of whether a state court could enforce a contract that was made in violation of a state statute. The case involved a contract between two parties, Kelley and Milan, in which Kelley agreed to pay Milan a certain amount of money for the sale of a piece of property. The contract was made in violation of a state statute that prohibited the sale of property without a license. The Supreme Court held that the state court could not enforce the contract because it was made in violation of the state statute. The Court reasoned that the state statute was a valid exercise of the state's police power and that the state had the right to protect its citizens from contracts that were made in violation of the law. The Court also noted that the state had the right to protect its citizens from contracts that were made without proper consideration. The Court's decision in Kelley v. Milan established that state courts could not enforce contracts that were made in violation of state statutes. This decision has been cited in numerous cases since then and has been used to support the idea that state courts should not enforce contracts that are made in violation of the law.

Justice Field delivered the dissenting opinion in Kelley v. Milan, arguing that the majority's decision was contrary to established precedent and would lead to an unjust result. He argued that under prior decisions of the Supreme Court, a party could not be held liable for damages if they had acted in good faith and without negligence when entering into a contract with another party. In this case, he noted that there was no evidence of fraud or bad faith on behalf of either party; thus, it should have been up to them alone to decide whether or not their agreement was validly formed. Furthermore, Justice Field argued that even if one were to assume some form of mistake had occurred during negotiations between both parties - which he did not believe had happened - then any resulting liability should fall solely upon the shoulders of whichever individual made such a mistake rather than being shared by both parties equally as proposed by the majority opinion.