What is the relationship between lying, belief, and knowledge? Prominent accounts of lying define it in terms of belief, namely telling someone something one believes to be false, often with the intent to deceive. This paper develops a novel account of lying by deriving evaluative dimensions of responsibility from the knowledge norm of assertion. Lies are best understood as special cases of vicious assertion; lying is the anti-paradigm of proper assertion. This enables an account of lying in terms of knowledge: roughly, lying is telling someone something you know ain't so.