What EU is and how it works

The union's edge is not the members' edge

Nine outermost regions sit inside the union and outside Europe. French Guiana, Guadeloupe, Martinique, Mayotte, Reunion and Saint-Martin belong to France, the Azores and Madeira to Portugal, and the Canary Islands to Spain. Article 349 of the Treaty on the Functioning of the European Union gives them a status of their own, and EU law applies there in full.

Thirteen Overseas Countries and Territories run the other way. They are associated with the union and are part of neither its territory nor its single market: Greenland under Denmark; Aruba, Bonaire, Curacao, Saba, Sint Eustatius and Sint Maarten under the Netherlands; French Polynesia, the French Southern and Antarctic Territories, New Caledonia, Saint Barthelemy, Saint Pierre and Miquelon, and Wallis and Futuna under France. The association dates from the Treaty of Rome in 1957 and rests on Articles 198 to 204. The records here carry the trace of it: the Netherlands lists the Aruban florin and the Caribbean guilder beside the euro, and France lists the CFP franc.

Getting in costs a ratification from everyone

Any European state may apply if it respects the union's democratic values and is committed to promoting them. What follows are the criteria set at the European Council in Copenhagen in 1993: stable institutions guaranteeing democracy, the rule of law, human rights and the protection of minorities; a functioning market economy able to cope with competitive pressure inside the union; and the ability to take on and implement the obligations of membership. The body of existing rules, the acquis, is then negotiated field by field. At the end an accession treaty is signed and ratified by the candidate and by every existing member state, so admission is not a decision the union takes about a country. It is a set of ratifications taken separately, and any one of them can stop it.

The dates on the member records show the shape that produced. Belgium, France, Italy, Luxembourg and the Netherlands carry 25 March 1957, the day the Treaty of Rome was signed, and Germany carries 1 January 1958, the day it took effect. Denmark and Ireland follow on 1 January 1973, Greece on 1 January 1981, Portugal and Spain on 1 January 1986, and Austria, Finland and Sweden on 1 January 1995. Ten states joined on 1 May 2004, Bulgaria and Romania on 1 January 2007, and Croatia on 1 July 2013.

Getting out has been done twice

Greenland left through a treaty of its own. It was signed on 13 March 1984 and came into force on 1 February 1985, and it stopped the Community treaties applying to Greenland, which took the status of an associated territory instead. Denmark did not leave, and Greenland is part of Denmark still.

The second exit went through Article 50 of the Treaty on European Union. The United Kingdom voted to leave on 23 June 2016, notified the European Council on 29 March 2017, and left at midnight Central European Time on 31 January 2020 after 43 years of membership. The withdrawal agreement came into force the following day and set a transition period running to 31 December 2020. The same departure cut the associated Overseas Countries and Territories from twenty-five to thirteen.

The inner circles do not line up with the membership

The euro has been the currency of 21 member states since Bulgaria adopted it on 1 January 2026. Denmark holds an opt-out written into the treaties and is not obliged to introduce it, and it is the only member that holds one. Czechia, Hungary, Poland, Romania and Sweden have not adopted it, and the Commission files them among the members that have yet to meet the conditions rather than among the exempt. Adoption came in steps: a first wave on 1 January 1999, Greece in 2001, Slovenia in 2007, Cyprus and Malta in 2008, Slovakia in 2009, Estonia in 2011, Latvia in 2014, Lithuania in 2015, Croatia in 2023.

Passport-free travel is wider than the union in one direction and narrower in another. Since Bulgaria and Romania joined on 1 January 2025 the Schengen area has stood at 29 countries: 25 member states, and Iceland, Norway, Switzerland and Liechtenstein, none of which is in the union at all. Ireland is exempted by the Schengen Protocol and runs its own visa and border policy. Cyprus takes part in Schengen cooperation and the Council has not yet abolished checks at its internal borders. The Bulgarian and Romanian records here carry 31 March 2024, the day checks were lifted at their air and sea borders, ahead of the land borders.

The seats are written into the treaties

Protocol No 6 fixes where the institutions sit, which means moving one takes a treaty amendment rather than a decision. The European Parliament has its seat in Strasbourg, where twelve periods of monthly plenary sessions are held, including the budget session; additional sessions and the committees meet in Brussels, and the secretariat stays in Luxembourg. The Council sits in Brussels and meets in Luxembourg during April, June and October. The Commission sits in Brussels. The Court of Justice, the Court of Auditors and the European Investment Bank sit in Luxembourg, the European Central Bank in Frankfurt, and Europol in The Hague.

Where the edges are argued

Cyprus joined whole and applies the rules in part. Protocol No 10 to the 2003 Act of Accession suspends the acquis in those areas of the Republic of Cyprus in which its government does not exercise effective control, and provides for that suspension to be withdrawn. The catalogue records the suspension and takes no position on the division underneath it.

Enlargement is not closed. Albania, Bosnia and Herzegovina, Kosovo, Montenegro, North Macedonia and Serbia are in the stabilisation and association process, which the Commission describes as the route by which those partners prepare for membership and which adds conditions on regional cooperation and good neighbourly relations. Nothing in it fixes a date, and this catalogue does not supply one.