"Nullum crimen nulla poena sine lege" is a Latin legal maxim that translates to "no crime, no punishment, without law." It means that there can be no criminal charge or punishment for an act unless a law has specifically defined it as a crime and prescribed a penalty.

This principle, also known as the principle of legality or the legality principle, is a fundamental aspect of many legal systems. It ensures that individuals are not punished for actions that were not illegal at the time they were committed and that laws are not applied retroactively.