The Treaty on European Union states among the objectives of the Union (Article 2):
to strengthen the protection of the rights and interests of the nationals of its Member States through the introduction of a citizenship of the Union;
Part two of the EU Treaty is called Citizenship of the Union, and it contains Articles 17 to 22.
Every person holding the nationality of a Member State shall be a citizen of the Union. Citizenship of the Union shall complement and not replace national citizenship (Article 17).
Every citizen of the Union shall have the right to move and reside freely within the territory of the Member States, subject to the limitations and conditions laid down in the Treaty and by measures adopted to give it effect (Article 18).
Further provisions have been given in Directive 2004/38/EC on the right of citizens of the Union and their family members to move and reside freely within the territory of the Member States. The aim of the Directive is that Union citizenship should be the fundamental status of nationals of the Member States when they exercise their right of free movement and residence.
Every citizen of the Union residing in another Member State has the right (on some conditions) to vote and to stand as candidate at municipal elections and in elections to the European Parliament, under the same conditions as nationals of that State (Article 19).
Every citizen of the Union is entitled to diplomatic and consular protection in a third country from any Member State, if his own country lacks representation there (Article 20).
Every citizen of the Union has the right to petition the European Parliament, apply to the Ombudsman and write to any of the EU institutions and bodies in any of the Treaty languages (Article 21).