Robertson v. Downing 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, Robertson and Downing, in which Robertson agreed to pay Downing 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 Robertson v. Downing 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.

In Robertson v. Downing, the Supreme Court was tasked with deciding whether a state court had jurisdiction to hear a case involving an alleged breach of contract between two citizens of different states. The majority opinion held that the state court did not have jurisdiction in this matter because it involved interstate commerce and thus fell under federal authority. Justice Field dissented from this decision, arguing that while Congress has power over interstate commerce, they do not have exclusive control over all matters related to it; rather, he argued that certain aspects still fall within the purview of individual states' courts. He further noted that if Congress were given exclusive control over such matters then there would be no need for any other judicial body besides them and their decisions could never be challenged or reviewed by another tribunal - something which is contrary to established legal principles and precedent.