This introductory chapter sheds new light on the increasingly complex relationship between the European Union and the nation-state—in its capacity as EU member state—at a time when its fundamental values are being called into question by prominent political currents. The chapter explores the concept of the nation-state in a contemporary European context and shows that tensions between supranationalism and intergovernmentalism are since long a defining feature of European integration. The chapter then introduces the book’s interdisciplinary approach which offers different disciplinary perspectives on how the return of the nation-state impacts the EU’s ability to meet the multifaceted challenges it is facing. The chapter concludes by arguing that the EU must take the tensions which arise from the strengthening of the nation-state seriously while actively standing up for the European political project, its basic legal principles and democratic values.