It has been 20 years since Union citizenship was introduced under the Treaty of Maastricht, yet it remains a topical and contemporary issue. The main research question underlying this study is whether and how European citizenship affects the constitutionalisation of the European Union. The present study connects European citizenship with European constitutional processes, in order to grasp the constitutional relevance of EU citizenship. To this end, the different aspects of European citizenship are specifically linked to features that are, commonly, found in constitutions. The effect of and relation between European citizenship and four of these constitutional ‘building blocks’ are assessed. First of all, the effect of European citizenship to the vertical division of powers between the Member States and the European Union is analysed. Second, the way European citizenship relates to a common ideology, existing of fundamental rights protection and democracy, is discussed. Moreover, the effect of European citizenship on judicial review and the hierarchy of norms in the European Union is addressed. Finally the question is posed how and to what extend European citizenship affects the constitutionalisation of the European Union and how European citizenship can be placed within the European constitutional context. Hanneke van Eijken (1981) holds Bachelor’s degrees in Law and Society (HU University of Applied Sciences Utrecht) and in Public Law (Utrecht University). She completed her Master’s programme in European Law at Utrecht University, with an honourable mention. She started working on her PhD thesis in 2008 under the supervision of Professor Professor Sacha Precha and judge of the European Court of Justice . During her research she made several research visits to the Court of Justice in Luxembourg and stayed at the European University Institute in Florence as a visiting researcher. Hanneke taught courses on International and European law, in the Netherlands and abroad. She was, moreover, assistant coordinator for the European Commission’s Network of Legal Experts in the Field of Gender Equality. She is member of the editorial board of the Nederlands Tijdschrift voor Europees recht. Since September 2013 she is a lecturer in European law at Utrecht University and works as a postdoctoral researcher for the BEUcitizen project. Outside the context of European law, Hanneke writes poetry and performs at literary festivals. Her collection of poetry was published in the spring of 2013 (‘Papieren veulens’, Prometheus, 2013), which has been nominated for and awarded literary prizes.