This article reports a test of a structural model of the antecedents of genocide and politicide (political mass murder). A case–control research design is used to test alternative specifications of a multivariate model that identifies preconditions of geno-/politicide. The universe of analysis consists of 126 instances of internal war and regime collapse that began between 1955 and 1997, as identified by the State Failure project. Geno-/politicides began during 35 of these episodes of state failure. The analytic question is which factors distinguish the 35 episodes that led to geno-/politicides from those that did not. The case–control method is used to estimate the effects of theoretically specified domestic and international risk factors measured one year prior to the onset of geno-/politicide. The optimal model includes six factors that jointly make it possible to distinguish with 74% accuracy between internal wars and regime collapses that do and those that do not lead to geno-/politicide. The conclusion uses the model to assess the risks of future episodes in 25 countries.This study was commissioned in 1998 by the Central Intelligence Agency's Directorate of Intelligence in response to President Clinton's policy initiative on genocide early warning and prevention. It was designed by the author and carried out using her data with other data and analytic techniques developed by the State Failure Task Force. Statistical analyses reported here were done by Michael Lustik and Alan N. Unger of Science Applications International Corporation (SAIC), McLean, Virginia. The author is senior consultant to the Task Force, which was established in 1994 in response to a request from senior U.S. policymakers to design and carry out a data-driven study of the correlates of state failure, defined to include revolutionary and ethnic wars, adverse or disruptive regime transitions, and genocides and politicides (for the latest report on Task Force research see Goldstone et al. 2002). The author acknowledges the advice of other Task Force consultants and analysts throughout the research process. The views expressed here are those of the author and do not represent the official views of the U.S. government, the U.S. intelligence community, or the Central Intelligence Agency.The author especially thanks Ted Robert Gurr for his critiquing early drafts and using the findings to construct the table that identifies high-risk countries and groups. His insistence about the importance of the study prompted me to revise the manuscript a number of times, despite my initial reluctance, given the years of work that had gone into its preparation. It was especially hard to condense this effort from its original 75 pages. The paper also benefited from a careful reading by Mark I. Lichbach of a previous report and from comments of anonymous reviewers for the American Political Science Review.