Despite a recent explosion of interest in the ethics of armed conflict, the traditional just war criterion that war be waged by a “legitimate authority” has received relatively little attention. Moreover, of those theorists who have addressed the criterion, many are deeply skeptical about its moral significance. This article aims to add some clarity and precision to the authority criterion and the debates surrounding it, and to suggest that this skepticism may be too quick. The first section analyzes the authority criterion and reveals that there are at least two distinct moral claims associated with it, each requiring separate evaluation. The second section outlines an increasingly influential “reductivist” approach to just war theory, explaining how this approach grounds powerful objections to the authority criterion. The third section sketches the most promising strategies for providing a qualified defense of authority, while acknowledging the further questions and complications these strategies raise. Importantly, the article aims to rehabilitate the authority criterion from within a broadly reductivist view.