The just war tradition is one of the key constituencies of international political theory, and its vocabulary plays a prominent role in how political and military leaders frame contemporary conflicts. Yet, it stands in danger of turning in on itself and becoming irrelevant. This article argues that scholars who wish to preserve the vitality of this tradition must think in a more open-textured fashion about its historiography. One way to achieve this is to problematize the boundaries of the tradition. This article pursues this objective by treating one figure that stands in a liminal relation to the just war tradition. Despite having a lot to say about the ethics of war, Xenophon is seldom acknowledged as a bona fide just war thinker. The analysis presented here suggests, however, that his writings have much to tell us, not only about how he and his contemporaries thought about the ethics of war, but about how just war thinking is understood (and delimited) today and how it might be revived as a pluralistic critical enterprise.