Abstract The aim of this article is to present a legal analysis of the concept of citizenship of the EU. This concept was considered by some to be embryonic in the original Community Treaties, but was first expressly incorporated into the Treaties by the Treaty on European Union, signed at Maastricht on 7 February 1992. In the case-law of the European Court of Justice, which has given citizenship a content going beyond the express Treaty provisions, the concept is closely related to other basic concepts, including free movement of persons, the prohibition of discrimination on grounds of nationality and the protection of fundamental rights. This article seeks to review the case-law, to disentangle citizenship from other related concepts, and to determine what added value citizenship has brought to the Treaties and what the potential and the proper limits of the concept might be.