Why do some postconflict states return to violence, while others remain at peace? Analysts increasingly credit postconflict justice institutions—such as truth commissions, amnesties, reparations, and trials—with contributing to the prevention of conflict recurrence following civil wars. But scholars remain divided about the overall effectiveness of these varied institutions. In this article, we directly engage this debate. We seek to overcome theoretical and data limitations that make it difficult to address the relationship between justice institutions and the likelihood that conflict will recur. We find that only postconflict justice processes that lessen conflict-induced grievances, and thus address individual motivations to rebel, are successful at keeping the peace.