Mobilizing in borderline citizenship regimes. A comparative analysis of undocumented migrants' collective actions 1 This article seeks to explain how and why groups and networks of undocumented migrants mobilizing in Berlin, Montreal and Paris since the beginning of the 2000s construct different types of claims. We explore the relationship between undocumented migrants and state authorities at the local level through the concept of the citizenship regime and its specific application to undocumented migrants (which we describe as the "borderline citizenship regime"). Despite their common formal exclusion from citizenship, non-status migrants experience different degrees and forms of exclusion in their daily lives, in terms of access to certain rights and services, recognition and belonging within the state (whether through formally or non-formally recognized means). As a result, they have an opportunity to create different, specific forms of leeway in the society in which they live. The concurrence of these different degrees of exclusion and different forms of leeway defines specific conditions of mobilization. We demonstrate how the content of their claims are influenced by these conditions of mobilization. Pierre Monforte is a Postdoctoral Fellow at the Centre de recherche sur les politiques et le Développement social (CPDS), University of Montreal. His work focuses on the mobilizations of migrants from a comparative perspective and on transnationalization processes. He obtained his PhD at the European