Double Jeopardy—the protection against repeated attempts by the state to convict a citizen for the same offense—is one of the core constitutional protections against false prosecution and the harassment of political opponents of the government. But we also have a federal system under our Constitution, in which the national and state governments are separate sovereigns who each perform independent functions. Does the separate sovereigns doctrine mean that Double Jeopardy applies to each accusation or to each government? If a state has brought a criminal prosecution, can the federal government do so as well? This question is not at all clear once we consider the principles behind the Double Jeopardy protection and the ramifications of a ruling one way or the other. The Court’s ruling will have long-term influence on the rights of criminal defendants and the ways in which jurisdictional battles are resolved in American law.