Nullum Crimen Sine Lege, Nulla Poena Sine Lege Law and Legal Definition

Nullum Crimen Sine Lege, Nulla Poena Sine Lege is a Latin maxim that means "no crime or punishment without a law." There can be no crime committed, and no punishment meted out, without a violation of penal law as it existed at the time. This basic legal principle has been incorporated into international criminal law.

In the U.S., this maxim finds expression in the Constitution by way of the Ex Post Facto Clauses, (U.S. Const. art. I, §§ 9, 10.) This principle of legality requires, as a prerequisite to just punishment, fair notice to the defendant of the conduct classified as criminal and the range of punishment attached to it. This principle also finds expression through the Due Process Clauses of the Fifth and Fourteenth Amendments by way of the "vagueness" doctrine, which is the requirement of reasonable precision in defining criminal conduct. The constitutional requirement of definiteness is violated by a criminal statute that fails to give a person of ordinary intelligence fair notice that his contemplated conduct is forbidden by the statute.