This article examines the role that military intervention can play in ending genocide and the political, moral, and legal debates that surround it. The first section briefly examines how genocides have ended since the beginning of the twentieth century, and explores the place of military intervention by external powers. The second section examines whether there is a moral and/or legal duty to intervene to end genocide. The third section considers the reasons why states intervene only infrequently to put an end to genocide despite their rhetorical commitments. Historically, once started, genocides tend to end with either the military defeat of the perpetrators or the suppression of the victim groups. Only military force can directly prevent genocidal killing, stand between perpetrators and their intended victims, and protect the delivery of lifesaving aid. But its use entails risks for all parties and does not necessarily resolve the underlying conflict.