In this article I defend a new argument against moralist theories of legitimacy and in favour of realist theories. Moralist theories, I argue, are vulnerable to ideological and wishful thinking because they do not connect the demands of legitimacy with the interests of rulers. Realist theories, however, generally do manage to make this connection. This is because satisfying the usual realist criteria for legitimacy – the creation of a stable political order that transcends brute coercion – is usually necessary for rulers to preserve their rule.