Migrant organizations are of vital importance for countries of residence and countries of origin, but the empirical and theoretical knowledge of the cross-border character of migrant organizations remains incomplete. It is clear that migrant transnationalism challenges the governance of nation-states on the local and national levels. This book, the outcome of an ECPR joint session, systematically and empirically analyzes the differing roles that transnational migrant organizations play in their countries of residence and origin. Drawing on research conducted in Belgium, England, Germany, Holland, Poland and Portugal, it focuses on the relations between migrant organizations and the state. Offering an opportunity for comparative analysis, it also examines why migrants and their organizations engage in different forms of border crossing activities, and how various political systems influence, and are influenced by these forms of engagement.