Processes of neoliberal globalization have put national trade unions under pressure as the transnational organization of production puts these labour movements in competition with each other. The global economic crisis has intensified these pressures further. And yet, economic and political integration processes have also provided workers with new possibilities to organize resistance. Emphasizing the importance of agency, this book analyzes transnational labour action in times of crisis, historically and now. It draws on a variety of fascinating cases, across formal and informal collectives, in order to clarify which factors facilitate or block the formation of solidarity. Moving beyond empirical description of cases to an informed understanding of collective action across borders, the volume provides an insightful theorization of transnational action.