Policymakers and scholars have turned their attention to federalism as a means for managing conflicts between central governments and subnational interests. But both the theoretical literature and the empirical track record of federations make for opposing conclusions concerning federalism's ability to prevent civil conflict. This article argues that the existing literature falls short on two accounts: first, it lacks a systematic comparison of peaceful and conflict-ridden cases across federal states, and second, while some studies acknowledge that there is no one-sizefits-all federal solution, the conditional ingredients of peace-preserving federalism have not been theorized. The authors make the argument that the peace-preserving effect of specific federal traits—fiscal decentralization, fiscal transfers, and political copartisanship—are conditional on a society's income level and ethnic composition. The argument is tested across twenty-two federal states from 1978 to 2000.