In a world in which change is constant, the principle of self-determination is important. Through (collective) acts of self-determination, nations exercise the right to govern themselves. At present the nation-state system with which we are familiar faces several challenges. In Western Europe, sub-state nationalism is on the rise. In the Middle East and North Africa, the state system bequeathed by former colonial powers faces increasing threats from pan-Islamist movements. Overall, the established order faces unprecedented uncertainties. The scholars who have contributed to this volume assess the merits, limitations and trajectories of self-determination in the twenty-first century, pointing to the paradoxes and anomalies that are encompassed by what at first sight is a simple and seductive concept. From the perspective of the twenty-first century and informed by a wealth of experience each of the contributors to this volume offers some valuable and intriguing observations on the future of self-determination and the movements its call engenders.This book was published as a special issue of Ethnopolitics.