This book explores the influences for ethnopolitical groups to act internationally in advancement of their group interests. Yu-Wen Chen proposes an ecological approach to comprehend ethnopolitical contention. In essence, she argues that transnationalizing the contention has the merit of raising the ethnopolitical group’s salience and helps to create niches that can demarcate one group from other claim-making groups in a society. Quantitative analysis of the primary data from the European Survey of Ethnopolitical Groups (ESEPG) and qualitative case studies confirm that although some ethnopolitical groups have presented their issues in the international arena, the domestic realm is still the main locus for ethnopolitical contention to occur. Salience, resources, domestic and international opportunity structures affect ethnopolitical groups’ international engagement. This book is an essential volume for anyone interested in ethnic mobilization, social movements, and transnationalization.