(CNN) -- Here is a look at what you need to know about the European Union.
About the European Union: The European Union is an international organization made up of 28 European countries.
It governs common economic, social and security policies of its member states.
According the EU website, the objectives of the EU are to establish European citizenship, ensure freedom, justice and security, promote economic and social progress, and assert Europe's role in the world.
Membership is open to any country with a democratic government, a good human rights record, and sound economic policies.
The member states delegate sovereignty to the EU institutions to represent the interests of the European Union as a whole.
Decisions and procedures stem from treaties ratified by the member states.
The capital of the European Union is Brussels, Belgium.
The EU is run by five main bodies: European Parliament, Council of the Union, European Commission, Court of Justice, and the Court of Auditors.
The European Union is a major economic unit. The combined population of member countries is 57% larger than that of the United States.
The United States is the EU's main trading partner.
The Treaty of Lisbon amends the Treaty on European Union to explicitly recognize for the first time the Member States' right to withdraw from the union. (Article 50, amended TEU) - Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements. - A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union.
Timeline: 1957 - The European Economic Community (EEC) is created. The member countries are Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany. "The goal was to remove trade barriers and form a common market."
1973 - Denmark, Ireland, and the U.K. become member countries.
1981 - Greece becomes a member.
1985 - Spain and Portugal become members
February 7, 1992 - The Treaty on the European Union is signed in Maastricht (Netherlands) by leaders of the member states.
November 1, 1993 - The Maastricht Treaty enters into force.
1993 - The EC members at the time (Belgium, France, Germany, Italy, Greece, Spain, UK, Luxembourg, the Netherlands, Denmark, Ireland, and Portugal) extend their cooperation into the areas of Justice and Home Affairs and a Common Foreign and Security Policy.
January 1, 1995 - Austria, Finland, and Sweden join the EU.
April 30, 2004 - A ceremony is held in Dublin, Ireland marking the expansion of the EU from 15 to 25 members. The new members are Poland, the Czech Republic, Slovakia, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, and Slovenia.
June 2004 - The member countries approve the text of the EU Constitution. It is signed by all the members in October 2004.
May 29, 2005 - The people of France (and its territories) vote against the European Union constitution in a referendum. (No = 54.87%/Yes = 45.13%)
June 1, 2005 - The Netherlands votes against the constitution in a referendum.
All 27 members of the EU must pass the constitution for it to take effect. Either a national parliament can approve it or in some countries, the citizens vote on a referendum.
June 23, 2007 - European Union leaders in Brussels agree on an outline of a treaty that would replace the EU constitution rejected by French and Dutch voters two years ago.
June 19, 2008 - European Union decides to lift diplomatic sanctions imposed on Cuba.
November 19, 2009 - Herman Van Rompuy, the Belgian Prime Minister, is Europe's first president under the Treaty of Lisbon. Catherine Ashton of the UK will be the first foreign minister.
December 1, 2009 - The Treaty of Lisbon comes into force, having been ratified by all European Union member states. It amends the Maastricht Treaty of 1992 and the Rome Treaty of 1957.
October 12, 2012 - Is awarded the Nobel Peace Prize for contributing to the advancement of peace, democracy and human rights in Europe.
July 1, 2013 - Croatia joins the EU as its 28th member.
April 1, 2014 - European Union launches military operations to restore stability to the Central African Republic.
Presidencies of the Council of the European Union until 2020: Greece: January-June 2014 Italy: July-December 2014 Latvia: January-June 2015 Luxemburg: July-December 2015 Netherlands: January-June 2016 Slovakia: July-December 2016 Malta: January-June 2017 United Kingdom: July-December 2017 Estonia: January-June 2018 Bulgaria: July-December 2018 Austria: January-June 2019 Romania: July-December 2019 Finland: January-June 2020
Current Members: (Founding members in bold) Austria Belgium Bulgaria Croatia Cyprus Czech Republic Denmark Estonia Finland France Germany Greece Hungary Ireland Italy Latvia Lithuania Luxembourg Malta Netherlands Poland Portugal Romania Slovakia Slovenia Spain Sweden United Kingdom
Candidate Countries: Iceland Former Yugoslav Republic of Macedonia Turkey
Applicant Countries: Albania Bosnia and Herzegovina Kosovo Montenegro Serbia