European Union citizenship is a novel and complex legal status. Since its formal conception in the Maastricht Treaty, EU citizenship has catalysed an extraordinary, and ongoing, legal experiment, the development and implications of which are traced comprehensively throughout this book. EU Citizenship Law articulates, explains, and analyses the legal framework and legal developments that have shaped the status of EU citizenship and the rights that it confers on Member State nationals. By examining how the rights and responsibilities produced by EU citizenship relate to other rights conferred by EU law, the distinctive meaning and scope – the added legal value – of EU citizenship is uncovered. But the legal story examined here sits in deeper and wider economic, political, social, and emotional contexts because EU citizenship is also an idea: a vector of European integration, collective personhood, and multi-layered identities that reflects the paradoxically inclusive and exclusive qualities of citizenship more generally. EU citizenship challenges us to consider the worth and deepen the protection of the person, and to shape a European Union where principles and values really matter. Thorough yet accessible, this work provides a comprehensive legal reference point for the progression of debates about what EU citizenship law actually ‘is, ‘ and for the continuing study and practice of EU citizenship law.