The introductory chapter provides an overview of the great social challenge that the EU currently faces. The editors raise the question of what can be done to bridge the prosperity gap in Europe. First, they briefly describe the background: the social dimension of European cooperation and its historical development. Second, they identify the new social challenges that the Union faces in the wake of the Great Recession, the ongoing refugee crisis, and the Brexit referendum. Third, an analytical point of departure for examining these challenges is presented, consisting of an interdisciplinary approach that pinpoints a number of overarching problems and possibilities associated with the social dimension of European integration. Fourth and finally, the book’s chapters are introduced, and their key policy recommendations are summarized. The chapter concludes with the argument that much of the EU’s future relevance and ability to stay together depends on its capacity to counteract the prosperity gap and reverse the negative trend that emerged during the crisis.