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").