<P> The European Union (EU) has expanded a number of times throughout its history by way of the accession of new member states to the Union . To join the EU, 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 . 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 . </P> <P> The EU's predecessor, the European Economic Community, was founded with the Inner Six member states 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 . </P> <P> As of 2018, accession negotiations are under way with Serbia (since 2014), Montenegro (since 2012) and Turkey (since 2005). Serbia and Montenegro have been described by President of the European Commission Jean - Claude Juncker and Enlargement commissioner Johannes Hahn as the front - runner candidates, and projected that they would join by 2025, during the next mandate of the European Commission . Negotiations with Turkey have also been ongoing at a slower pace, particularly since the 2016 Turkish coup d'état attempt due to objections from the EU to the Turkish government's response . Additionally, the United Kingdom is negotiating its withdrawal from the EU, following a referendum in which a majority voted in favour of leaving the EU . </P>

Which country was the last to join the eu