Ignorantia juris non excusat

In law, ignorantia juris non excusat (Latin for 'ignorance of the law excuses not'), or ignorantia legis neminem excusat ('ignorance of law excuses no one'), is a legal principle holding that a person who is unaware of a law may not escape liability for violating that law merely by being unaware of its content.

European-law countries with a tradition of Roman law may also use an expression from Aristotle translated into Latin: nemo censetur ignorare legem ('nobody is thought to be ignorant of the law') or ignorantia iuris nocet ('not knowing the law is harmful').