The article presents a comparative analysis of genocide in Rwanda and Darfur. The first half of the article examines the patterns and origins of violence in both cases and uses the comparison to generate some theoretical inferences about the causes of genocide. The analysis finds that both cases demonstrate a similar character of violence but that in Rwanda the violence was more intense, more exterminatory, and more participatory than in Darfur. Both episodes took place in the midst of civil war, in periods of political transition, in countries with histories of ethnic nationalism, and in areas where the conflicting ethnic populations lived in relative proximity. However, in Rwanda the state is more compact, centralized, and effective, which may explain the variation in intensity. The second half of the article focuses on the international response to genocide in both cases. After Rwanda, observers emphasized the importance of using the label "genocide" and creating domestic constituencies. Darfur showed that both strategies are insufficient. In response to Darfur, US officials declared "genocide" to be occurring, and there emerged a politically diverse civil-society coalition to lobby the administration. Yet the net outcome for both cases, in terms of the absence of an effective policy to halt genocide, was the same. The article argues that focusing too intently on a "genocide" determination may be counterproductive, that international politics matter yet mobilization on Darfur outside of North America was weak, and that protocols for the use of force to prevent genocide should be clarified.