Enlargement of the European Union

The process of expanding the European Union (EU) through the accession of new member states began with the Inner Six, who founded the European Economic Community (the EU's predecessor) in 1958, when the Treaty of Rome came into force. Since then, the EU's membership has grown to twenty-eight, with the latest member state being Croatia, which joined in July 2013.

The most recent territorial enlargement of the EU was the incorporation of Mayotte in 2014. The most notable territorial reductions of the EU, and its predecessors, were the exit of Algeria upon independence in 1962 and the exit of Greenland in 1985.

Currently, accession negotiations are under way with several states. The process of enlargement is sometimes referred to as European integration. This term is also used to refer to the intensification of co-operation between EU member states as national governments allow for the gradual harmonisation of national laws.

To join the European Union, a state needs to fulfil economic and political conditions called the Copenhagen criteria (after the Copenhagen summit in June 1993), which require a stable democratic government that respects the rule of law, and its corresponding freedoms and institutions. According to the Maastricht Treaty, each current member state and the European Parliament must agree to any enlargement.