Advocates of wartime international criminal tribunals (ICTs) hope that such tribunals can deter combatant atrocities against civilians. Yet, more than twenty-five years after the establishment of the first wartime ICT—the International Criminal Tribunal for the former Yugoslavia (ICTY)—wartime ICTs’ role in deterring such violence remains a matter of debate. Insights from criminology, as well as research on civil conflicts and international legal compliance, suggest that ICTs are most likely to deter government and rebel forces from committing atrocities against civilians when all three of the following conditions are present: (1) ICT officials have secured sufficient prosecutorial support, (2) combatant groups rely on support from liberal constituencies, and (3) combatant groups have centralized structures. Case studies of the ICTY's impact on fourteen combatant groups from the Yugoslav conflicts—combined with hundreds of field interviews with war veterans and others—confirm this prediction. The ICTY's record thus sheds important light on how and when contemporary wartime ICTs—including the International Criminal Court—might succeed in deterring combatant atrocities against civilians.