How do armed groups use violence to create social ties? What are the conditions under which such violence takes place? In this article, I describe how armed groups use one type of atrocity, wartime rape, to create social bonds between fighters through a process of combatant socialization. As a form of stigmatizing, public, and sexualized violence, gang rape is an effective method to communicate norms of masculinity, virility, brutality, and loyalty between fighters. Drawing on literature about socialization processes, I derive a set of hypotheses about individual-level factors that may influence vulnerability to violent socialization, including age, previous socialization experiences, and physical security. I analyze the support for these hypotheses using newly available survey data from former fighters in the Democratic Republic of the Congo. The results show the broad applicability of considering group violence as a form of social control within armed groups, suggest some of the limits of violent socialization, and have implications for both theory and policy.