Nulla Poena Sine Lege

Nulla Poena Sine Lege is a legal principle that asserts that no individual can be punished under criminal law unless their conduct was clearly defined as punishable by law at the time of the offense. This principle protects individuals from ex post facto laws and ensures that legal penalties are strictly defined by pre-existing statutes.

This maxim has its roots in Roman law and has been a fundamental concept in legal systems that adhere to the rule of law, particularly within Western legal traditions. It reflects a commitment to fairness and predictability in the legal system.

In modern law, Nulla Poena Sine Lege is applied to prevent retroactive legislation that would impose penalties for actions that were not illegal at the time they were committed. It is a cornerstone in criminal law, reinforcing the requirement for clarity and specificity in penal statutes to protect individuals' rights.

• A law is enacted making it illegal to engage in a specific activity, but anyone who engaged in that activity before the law was passed cannot be prosecuted for it.
• If a person is charged with a crime that was not defined or described in law, they cannot be punished for it, even if the action was broadly considered immoral.

• The U.S. Supreme Court case of Bouie v. Columbia (1964) emphasizes the principle as a safeguard against arbitrary enforcement of law.