The Treaty on European Union, commonly known as the Maastricht Treaty, is the foundation treaty of the European Union (EU). Concluded in 1992 between the then-twelve member states of the European Communities, it announced "a new stage in the process of European integration" chiefly in provisions for a shared European citizenship, for the eventual introduction of a single currency, and for common foreign and security policies, and a number of changes to the European institutions and their decision taking procedures, not least a strengthening of the powers of the European Parliament and more majority voting on the Council of Ministers. Although these were seen by many to presage a "federal Europe", key areas remained inter-governmental with national governments collectively taking key decisions. This constitutional debate continued through the negotiation of subsequent treaties, culminating in the 2007 Treaty of Lisbon.

The European Union (EU) is a supranational political and economic union of 27 member states that are located primarily in Europe. The Union has a total area of 4,233,255 km2 (1,634,469 sq mi) and an estimated total population of over 448 million. The EU has often been described as a sui generis political entity combining the characteristics of both a federation and a confederation.