Ellingburg challenged restitution imposed under the Mandatory Victims Restitution Act for conduct predating the statute’s application to his offense. The Supreme Court held that mandatory restitution under the MVRA is criminal punishment for purposes of the Ex Post Facto Clause. Restitution is imposed as part of the criminal judgment, serves punitive as well as compensatory purposes, and is enforced through the criminal process. A later statute that increases or newly mandates that punishment therefore may not be applied retroactively to earlier conduct. The judgment was reversed and the case remanded.