Nulla poena sine lege

Nulla poena sine lege (Latin for "no penalty without law", Anglicized pronunciation: /ˈnʌlə ˈpiːnə ˈsaɪniː ˈliːdʒiː/ NUL-ə PEE-nə SY-nee LEE-jee) is a legal formula which, in its narrow interpretation, states that one can only be punished for doing something if a penalty for this behavior is fixed in criminal law. As some laws are unwritten (e.g. in oral law or customary law) and laws can be interpreted broadly, it does not necessarily mean that an action will not be punished simply because a specific rule against it is not codified.

The variant nullum crimen sine lege ("no crime without law") establishes that conduct is not criminal if not found among the behavior/circumstance combinations of a statute. The other interpretations of the formula include the rules prohibiting retroactive criminalization and prescribing laws to be strictly construed.^[1]

Despite the use of Latin language and brocard-like^[2] appearance, the formula was mostly born in 18th century liberalism (some elements of non-retroactivity of laws and limiting the punishment to the one prescribed in the statute date back to Roman times).^[3] This principle is accepted and codified in modern democratic states as a basic requirement of the rule of law.^[4] It has been described as "one of the most 'widely held value-judgement[s] in the entire history of human thought'".^[5]