Exploring the notion that norms are often seen as static structures governing society, politics and legislation, this thought-provoking book offers insights into Robert Alexy's theory of constitutional rights and the range in rigidity of two norm categories: rules and principles. Arguing that constitutional pluralism and the differentiation between norms is also present in EU law, Anne Wesemann asserts that EU Citizenship is a principle and thus a constitutional rights norm. Providing new perspectives on constitutionalism in the EU, this book considers the way the Court of Justice of the European Union (CJEU) discusses and applies the EU citizenship Treaty norms by analysing the court's approach to decision making, which mirrors the balancing and weighing of conflicting principles. Wesemann proposes a new approach to constitutional analysis of the EU and its legal framework, arguing that the existence of constitutional rights norms in EU law enables this particular legal order to respond effectively to societal and political challenges within the rigidity of constitutionalism. Citizenship in the European Union will be a key resource for scholars and students of constitutional law and politics. Its contribution to the discourse around judicial activism and politicisation will also be essential reading for those studying the workings of the CJEU.