The criminal law is part of the police power— the power to protect the public health and safety— that was shared between the states and the federal government. Historically, federal criminal law dealt with uniquely federal issues such as antitrust activities by interstate corporations, income tax evasion, treason, and specific crimes such as federal civil rights violations that did not exist under state law. The last several decades have seen the expansion of federal criminal law into areas such as narcotics dealing that are also prosecuted by the states and development of state parallels with federal civil rights laws. The result is that state and federal powers now overlap to such an extent that many crimes can be prosecuted by either authority, and sometimes both.

Criminal law is used to protect individuals both for their own good and to protect the social order that makes it possible to govern. Criminal prosecution redresses the injury to the state by punishing the defendant and deters future criminal activity by the example of the defendant and by the practical expedient of keeping defendants in prison where they cannot commit new crimes against society. Individuals who are injured by crimes can bring civil (tort) litigation against the criminal for compensation. Except in the rarest of circumstances, the individual cannot bring a criminal prosecution but must persuade the police or the state’s attorney to bring the prosecution. The state may choose to not prosecute despite the victim’s evidence and the state may choose to prosecute even if the victim does not want the defendant prosecuted. Unlike in civil litigation, these choices are reserved to the state because the criminal prosecution is ultimately about protecting the state, rather than individuals. Criminal laws are enforced by the government in its own name: United States v. Salerno, or Texas v. Powell.