Case studies suggest that ethnic groups with autonomous institutional arrangements are more prone to secede, but other evidence indicates that autonomy reduces the likelihood of secession. To address this debate, we disaggregate their autonomy status into three categoriescurrently autonomous, never autonomous, and lost autonomy-and then unpack how each shapes the logic of collective action. We argue groups that were never autonomous are unlikely to mobilize due to a lack of collective action capacity, whereas currently autonomous groups may have the capacity but often lack the motivation. Most important, groups that have lost autonomy often possess both strong incentives and the capacity to pursue secession, which facilitates collective action. Moreover, autonomy retraction weakens the government's ability to make future credible commitments to redress grievances. We test these conjectures with data on the autonomous status and separatist behavior of 324 groups in more than 100 countries from 1960 to 2000. Our analysis shows clear empirical results regarding the relationship between autonomy status and separatism. Most notably, we find that formerly autonomous groups are the most likely to secede, and that both currently autonomous and never autonomous groups are much less likely. Keywords nationalism, separatism, decentralization, autonomy Does autonomy satisfy the demand for more self-determination, or instead foster the capacity and whet the appetite for independence? Is political 2 Comparative Political Studies XX(X) decentralization a viable solution for multiethnic states, or a slippery slope? Some scholars and policymakers see autonomy as the main mechanism to resolve tensions and redistributive issues between the central government and spatially concentrated, culturally distinct groups (Bermeo, 2002;Bermeo & Amoretti, 2003;L. Diamond, 1999;Stepan, 1999). Others studies, however, show that autonomy can actually exacerbate relations between the state and ethnic groups, for it cultivates the capacity for collective action and self-rule without significantly reducing desire for more of it (Brancati, 2009;Bunce, 1999;Coppieters, 2001;Cornell, 2002;Roeder, 1991).This article posits that the theoretical and empirical disagreement over the effect of autonomy is partly due to conflating two distinct situations in the implicit reference category-groups that are not autonomous. This binary classification compares groups that are currently autonomous to a baseline that is comprised of both groups that have never been autonomous, and those that once had autonomy, but lost it. Groups that have never been autonomous and those that have lost autonomy are distinct in their motivation and their capacity for collective action. Whereas never autonomous groups may be unlikely to mobilize due to a lack of collective action capacity, currently autonomous groups may have such capacity, but should find the cost of attempting to alter the status quo too high compared with the benefits they currently enjoy from being auton...