Citizenship of the Union
European citizenship was referred to in the Treaty of Maastricht in 1993.This was the Treaty "on" European union, not "of" Union. It did not set up a supranational European Union, with full legal personality of its own. The European Community continued as the supranational entity.
Real EU citizenship derives from the Treaty of Lisbon. The Lisbon Treaty states that EU citizenship is "additional" to national citizenship instead of being "complementary" to it, as referred to in the Maastricht Treaty. An additional citizenship is a true dual citizenship so that EU citizens will be both national and EU citizens. This is because under the Lisbon Treaty the Union has its own iegal personality separate from those of its Member States and can have individuals as its real citizens for the first time.This is the normal position in federal states such as Germany or the USA.
EU citizenship prevails over national citizenship in the same way as, for example, German citizenship prevails over that of Bavaria. Therefore, Bavarians have a triple citizenship: one from Bavaria, one from Germany, and then EU citizenship.
The new additional citizenship is connected to the Charter of Fundamental Rights which can be further developed by the Council of Ministers and the EU Court. The rights of EU citizenship are defined in Arts. 20 - 25 TFEU of the Lisbon Treaty.
Denmark has a derogation from the concept of joint citizenship. The new article on "additional" citizenship is not translated into the Danish edition of the treaty, which continues to refer to "complementary" citizenship only.
Links
Scadplus: Citizenship of the Union http://europa.eu/scadplus/leg/en/s18000.htm