I argue that the rarely discussed Antichrist can serve as perhaps the best guide to Nietzsche’s mature ethical theory. Commentators often argue or assume that while Nietzsche makes many critical points about traditional morality, he cannot be offering a positive ethical theory of his own. This, I argue, is a mistake. The Antichrist offers a substantive ethical theory. It explicitly articulates Nietzsche’s positive ethical principles, shows why these principles are justified, and uses them to condemn traditional Christian morality. The chapter reviews and explains Nietzsche’s ethical theory. It also considers why commentators so often assume that Nietzsche cannot have an ethical theory: I argue that commentators tend to be driven by the assumption that all ethical theories embrace seven commitments. These commitments are, I suggest, definitive of Enlightenment ethical theory, but not of ethical theory as such; Nietzsche’s rejection of them in no way precludes his having a positive ethical theory of his own.