The European Union (EU) is an economic and political union of 27 member states,[9] located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993 upon the foundations of the European Communities.[10] With over 500 million citizens,[11] the EU combined generates an estimated 30% share (US$ 18.4 trillion in 2008) of the nominal gross world product and about 22% (US$15.2 trillion in 2008) of the PPP gross world product.[12]

The EU has developed a single market through a standardised system of laws which apply in all member states, ensuring the free movement of people, goods, services, and capital.[13] It maintains common policies on trade,[14] agriculture, fisheries[15] and regional development.[16] Sixteen member states have adopted a common currency, the euro, constituting the Eurozone. The EU has developed a limited role in foreign policy, having representation at the World Trade Organization, G8, G-20 major economies and at the United Nations. It enacts legislation in justice and home affairs, including the abolition of passport controls by the Schengen Agreement between 22 EU and 3 non-EU states.[17]

As an international organisation, the EU operates through a hybrid system of supranationalism and intergovernmentalism.[18][19][20] In certain areas, decisions are made through negotiation between member states, while in others, independent supranational institutions are responsible without a requirement for unanimity between member states. Important institutions of the EU include the European Commission, the Council of the European Union, the European Council, the Court of Justice of the European Union, and the European Central Bank. The European Parliament is elected every five years by member states' citizens, to whom the citizenship of the European Union is guaranteed.

The EU traces its origins from the European Coal and Steel Community formed among six countries in 1951 and the Treaty of Rome formed in 1957 by the same states. Since then, the EU has grown in size through enlargement, and in power through the addition of policy areas to its remit.