What does it mean to be a European citizen? From the treatise, the question is easily answered: Being a European citizen means being a citizen of a Member State of the European Union (EU). Outside the treatise, however, the question is at the core of a significant (r)evolution. From the last years, the European Parliament, the European Commission, and the European Court of Justice are all newly and increasingly paying attention to the very substance of the legal link between the EU and its citizens.