Ancient philosophers offer intriguing accounts of vice – virtue's bad twin. This Element considers injustice and lawlessness in Plato and Aristotle. Starting with Socrates' paradoxical claim that 'tyrants and orators do just about nothing they want to do' (Gorgias 466d-e), it examines discussions of moral ignorance and corruption of character in Plato's Republic and Aristotle's Nicomachean Ethics. Aristotle's account of vice is indebted to Plato's. But his claims have confounded critics. Why is the vicious agent full of regrets when he acts in accordance with his wish? To what extent is vice a form of moral ignorance? Why will the unjust man never get what he wants? These and other questions yield new insights into ancient Greek ethics and moral psychology, as well as surprising perspectives on contemporary debates.