The legal concept of citizenship of the (European) Union was formally introduced into the EC Treaty in 1993 by the Treaty of Maastricht. It is now addressed in Part II of the Treaty on the Functioning of the European Union (Articles 20-24). Citizenship is also given a formal constitutional status in the EU legal order, through its inclusion in Article 9 of the Treaty of European Union which provides that "Every national of a Member State shall be a citizen of the Union. Citizenship of the Union shall be additional to and not replace national citizenship.”
Accordingly, the status is determined by reference to Member State nationality: all (and only) Member State nationals are European Citizens. Member States have a largely unfettered power to determine the scope of their own nationality law, and thus (collectively) to control who are the citizens of the European Union. However, since the ruling of the CJEU in 2010 in the case Janko Rottmann v Freistaat Bayern, it has been confirmed that Member States must have due regard to the status of European Citizenship when determining matters of nationality.
European Citizens enjoy a bundle of legal rights by virtue of their status. The vast majority of these rights are enjoyed by mobile European Citizens who have exercised rights of free movement throughout the Union. Amongst the most important of these are electoral rights. A limited number of rights may be relied upon by European Citizens against their Member State of nationality in the absence of cross-border movement. The decision of the CJEU in Ruiz Zambrano v Office National de L'emploi, in which a Member State was required to grant a work permit to the third-country national carer of a European Citizen who had yet to exercise his right of free movement throughout the Union, so as not to deprive the European Citizen of the genuine enjoyment of the substance of his rights, proved a significant development in this regard.
This section of the website contains a selection of legislation, policy documents, case law, publications and references concerning European Citizenship. The selected documents are intended to reflect central developments in the status of European Citizenship. They encompass, in particular, documents relevant to the relationship between national and European Citizenship and to the exercise of the electoral rights enjoyed by European Citizens.
This informarion is taken from this link.