Highly active citizens assume responsibility in politics and the civil society; for example, by organising social groups and activities, and lobbying on government policies. Although first-generation immigrant activists are a small minority in European societies, they are of critical importance for the receiving societies’ democratic development. The POLITIS project conducted the first study that focused exclusively on this crucial group. This book both provides an overview of theoretical discussions and empirical conditions that frame immigrants’ activities and presents the major results of the study based on extensive interviews with more than 170 immigrants active in 24 EU member states. The book’s final section offers careful reflections on the study’s results and considers implications for social scientists, policy makers, and activists in NGOs and immigrant organisations.