Potential enlargement of the European Union

The 2003 European Council summit in Thessaloniki set the integration of the Western Balkans as a priority of EU expansion. This commitment was made in order to stabilise the region in the wake of the Yugoslav Wars, a series of ethnic wars through the 1990s that led to the break-up of Yugoslavia.

Slovenia was the first former Yugoslav country to join the EU in 2004, followed by Croatia in 2013.

Albania, Serbia, North Macedonia, and Montenegro are all candidate states, and all of them are in negotiations.[15] Bosnia and Herzegovina has applied to join but is not yet recognised as a candidate while Kosovo, which declared independence in 2008, is not recognised by 5 EU states or by Serbia.

Serbia and Montenegro could join the EU in 2025.[16] The European Council endorsed starting negotiations with Albania and North Macedonia on 26 March 2020, and they could join after 2025.[17]

Bulgaria blocked North Macedonia's EU Accession Negotiations.[18]

Turkey's candidacy to join the EU has been a matter of major significance and considerable controversy since it was granted in 1999. Turkey has had historically close ties with the EU, having an association agreement since 1964,[19] being in a customs union with the EU since 1995 and initially applying to join in 1987. Only after a summit in Brussels on 17 December 2004 (following the major 2004 enlargement), the European Council announced that membership negotiations with Turkey were officially opened on 3 October 2005.

Turkey is the eleventh largest economy in the world, and is a key regional power.[20][21] In 2006, Carl Bildt, former Swedish foreign minister, stated that "[The accession of Turkey] would give the EU a decisive role for stability in the Eastern part of the Mediterranean and the Black Sea, which is clearly in the strategic interest of Europe."[22]

However, others, such as former French President Nicolas Sarkozy and former German Chancellor Angela Merkel, opposed Turkey's membership. Opponents argue that Turkey does not respect the key principles that are expected in a liberal democracy, such as the freedom of expression.[23] Turkey's large population would also alter the balance of power in the representative European institutions. Upon joining the EU, Turkey's 84 million inhabitants would bestow it the largest number of MEPs in the European Parliament. It would become the most populous country in the EU.[24] Another problem is that Turkey does not recognise one EU state, Cyprus, because of the Cyprus dispute and the Cypriot government blocks some chapters of Turkey's talks.

Turkey's relations with the EU have seriously deteriorated in the aftermath of the 2016 Turkish coup d'état attempt and subsequent purges.[25][26] On 24 November 2016, the European Parliament approved a non-binding resolution calling for the "temporary freeze of the ongoing accession negotiations with Turkey" over human rights and rule of law concerns.[27][28][29] On 13 December, the European Council (comprising the heads of state or government of the member states) resolved that it would open no new areas in Turkey's membership talks in the "prevailing circumstances",[30] as Turkey's path toward autocratic rule made progress on EU accession impossible.[31] As of 2022, and especially following Erdoğan's victory in the constitutional referendum, Turkish accession talks are effectively at a standstill.[4][32][33]

Georgia, Moldova, and Ukraine ratified an Association Agreement with the EU, and the European Parliament passed a resolution in 2014 stating that "in accordance with Article 49 of the Treaty on European Union, Georgia, Moldova and Ukraine, as well as any other European country, have a European perspective, can apply for EU membership in compliance with the principles of democracy, respect for fundamental freedoms and human rights, minority rights and ensuring the rule of rights."[34] They also entered the Deep and Comprehensive Free Trade Area with the EU, which creates "framework for modernising [...] trade relations and for economic development by the opening of markets via the progressive removal of customs tariffs and quotas, and by an extensive harmonisation of laws, norms and regulations in various trade-related sectors, creating the conditions for aligning key sectors" of their economies with EU standards.[35] However, the EU did not expand further into the post-Soviet space in the 2010s.[36]

By January 2021, Georgia and Ukraine were preparing to formally apply for EU membership in 2024.[37][38][39] However, following the 2022 Russian invasion of Ukraine, Ukraine submitted an application for EU membership on 28 February 2022, followed by Georgia and Moldova on 3 March 2022.[40][41]

States in Europe who have chosen, for various reasons, not to join the EU have integrated with it to different extents according to their circumstances. Iceland, Norway, and Liechtenstein participate directly in the single market via the EEA, Switzerland does so via bilateral treaties and the other European microstates (Andorra, Monaco, San Marino, Vatican City) have specific agreements with the EU and neighbouring countries, including their use of the euro as their currency. Most of these countries are also part of the Schengen Area. Norway, Iceland, and Switzerland have all previously had live applications to join the EU, which have been withdrawn or otherwise frozen. Such applications could be resubmitted in the event of a change in the political landscape.

Armenia
	Main article:	Armenia–European Union relations
	Relationship:	Armenia-EU Comprehensive and Enhanced Partnership Agreement.[104]
	Main obstacles:	Dispute with Azerbaijan regarding Artsakh/Nagorno-Karabakh.
	Proponents:	Bright Armenia, European Party of Armenia,[105] Free Democrats, Heritage,[106] People's Party of Armenia,[107] Republic Party, Rule of Law,[108] Union for National Self-Determination[109]
	Opponents:	Nikol Pashinyan,[110] Prosperous Armenia[111]
	Public opinion:	40% in favour, 11% against (2020 poll)[112]
Belarus
	Main article:	Belarus–European Union relations
	Relationship:
	Main obstacles:	Alexander Lukashenko's authoritarian rule, Russian political influence, Union State (integration with Russia).
	Proponents:	Belarusian Christian Democracy, BPF Party, United Democratic Forces of Belarus, Belarusian Liberal Party of Freedom and Progress, United Civic Party of Belarus, Belarusian Social Democratic Party (Assembly), Belarusian Social Democratic Assembly
	Opponents:	Russian government, Alexander Lukashenko
	Public opinion:	42.1% in favour (2013 poll with several options)[113]
Iceland
	Main article:	Iceland–European Union relations
	Relationship:	Member of the European Economic Area and Schengen Area, frozen membership application.
	Main obstacles:	Common Fisheries Policy[114] and others.
	Proponents:	Social Democratic Alliance, Reform Party, Bright Future
	Opponents:	Independence Party, Left-Green Movement, Progressive Party
	Public opinion:	47% in favour, 33% against (2022 poll).[115]
Norway
	Main article:	Norway–European Union relations
	Relationship:	Member of the European Economic Area and Schengen Area, frozen application, but not withdrawn.
	Main obstacles:	Common Fisheries Policy and others, public opinion.
	Proponents:	Conservative Party, Labour Party, Liberal Party
	Opponents:	Progress Party, Centre Party, Red Party, Socialist Left Party
	Public opinion:	26% in favour, 53% against (2022 poll).[116]
Russia
	Main article:	Russia–European Union relations
	Relationship:
	Main obstacles:	Vladimir Putin's authoritarian rule, Eurosceptic government, and occupation of Georgia, Moldova, and Ukraine.
	Proponents:	Yabloko, People's Freedom Party, Russia of the Future, Democratic Party of Russia, 5th of December Party, Green Alternative
	Opponents:	Vladimir Putin, United Russia
	Public opinion:
San Marino
	Main article:	San Marino–European Union relations (Microstates and the European Union)
	Relationship:	Bilateral treaties, open border, customs union, and euro adoption.
	Main obstacles:	Small size.[117]
	Proponents:	United Left,[118] Union for the Republic,[119] Civic 10,[120][121] Party of Socialists and Democrats,[122] Socialist Party,[123] For San Marino[124][125]
	Opponents:	Sammarinese Christian Democratic Party,[126] Sammarinese Social Right Movement
	Public opinion:	A referendum in 2013 on applying for EU membership resulted in 50.3% approving, but it failed due to insufficient turnout.[127]
Switzerland
	Main article:	Switzerland–European Union relations
	Relationship:	Bilateral treaties allowing participation in the European Single Market, member of the Schengen Area, withdrawn membership application.
	Main obstacles:	Swiss public opinion and direct democracy.
	Proponents:	Green Party, Social Democratic Party,[128] Green Liberal Party[129]
	Opponents:	Swiss People's Party, Evangelical People's Party, Ticino League, Federal Democratic Union, Swiss Party of Labour, Solidarity,[129] Campaign for an Independent and Neutral Switzerland[130][131]
	Public opinion:	A Swiss referendum on restarting EU membership negotiations in 2001 was defeated by 76.8%.[132]
United Kingdom (Including  Gibraltar)
	Main article:	United Kingdom–European Union relations
	Relationship:	Withdrawal agreement, EU–UK Trade and Cooperation Agreement, past membership.
	Main obstacles:	Recent withdrawal and government policy.
	Proponents:	Liberal Democrats,[133] Volt UK[134]
	Opponents:	Conservative Party, Reform UK
	Public opinion:	Polling on the UK rejoining the EU

• Andorra, Liechtenstein, Monaco, and Vatican City are European microstates that are not on the agenda of the EU to be members, nor their own. See: Microstates and the European Union.
• Azerbaijan and Kazakhstan are transcontinental states. These countries are not on the agenda of the EU to be members, nor their own. See: Azerbaijan–European Union relations and Kazakhstan–European Union relations.
• Canada is a non-European country with values, culture, trade, and politics closely linked with the EU. Its membership has been proposed due to this. See: Canada–European Union relations.
• Cape Verde and Israel are non-European countries with close historical and political relations with the EU. See: Cape Verde–European Union relations and Israel–European Union relations.
• The Order of Malta is a sovereign entity without territory that has extraterritorial headquarters in Palazzo Malta and Villa Malta, as well as observer status in the United Nations and the Council of Europe. See: Sovereign Military Order of Malta–European Union relations.

Despite Scotland voting to stay,[135] the United Kingdom as a whole left the European Union in 2020, leaving potential future membership for Scotland as enlargement from outside of the EU.[136] The Scottish National Party (SNP) which leads Scotland's devolved government supports re-joining the EU should Scotland become independent in the future.[137]

On 1 October 2017, the Catalan government held a referendum on independence, which had been declared illegal by the Constitutional Court of Spain, with potential polling stations being cordoned off by riot police. The subsequent events constituted a political crisis for Catalonia. The EU's position is to keep distance from the crisis while supporting Spain's territorial integrity and constitution.[154][155] While the debate around Scotland's referendum may inform the Catalan crisis, Catalonia is in a distinct situation from Scotland whereby the central government does not recognise the legitimacy of any independence declaration from Catalonia. If Spain does not recognise the independence of a Catalan state, Catalonia cannot separately join the EU and it is still recognised as part of Spain's EU membership.

Corsica has a strong and electorally successful nationalist movement, with positions ranging from autonomy to outright independence, the latter option with around 10–15% public support.[156] The independist party Corsica Libera envisions an independent Corsica within the European Union as a union of various European peoples, as well as recommendations for alignment within European directives.[157]

There is an active movement towards Flemish independence or union with the Netherlands. The future status of Wallonia and Brussels (the de facto capital of the EU) are unclear as viable political states, perhaps producing a unique situation from Scotland and Catalonia. There are various proposals, both within and outside the independentist movement, for what should happen to Brussels, ranging from staying part of the Belgian rump state, to joining the hypothetical Flemish state, to becoming a separate political entity.[158][159]

Sardinia has a strong and electorally successful nationalist movement, with positions ranging from autonomy to outright independence.

As the Sardinian movement has its origins on the left of the political spectrum[160][161] It is mostly pro-european, with a key focus on environmentalism.

According to a 2012 survey conducted in a joint effort between the University of Cagliari and that of Edinburgh,[162][163][164] 41% of Sardinians would be in favour of independence (with 10% choosing it from both Italy and the European Union, and 31% only from Italy with Sardinia remaining in the EU), whilst another 46% would rather have a larger autonomy within Italy and the EU, including fiscal power; 12% of people would be content to remain part of Italy and the EU with a Regional Council without any fiscal powers, and 1% in Italy and the EU without a Regional Council and fiscal powers.[165][166][167][168][169][170][171] A 2017 poll by the Ixè Institute found that 51% of those questioned identified as Sardinian (as opposed to an Italian average of 15% identifying by their region of origin), rather than Italian (19%), European (11%) and/or citizen of the world (19%).[172][173]

Sardinian nationalists address a number of issues, such as the environmental damage caused by the military forces[174][175][176][177][178][179][180][181][182] (in fact, 60% of such bases in Italy are located on the island),[183] the financial and economic exploitation of the island's resources by the Italian state and mainland industrialists,[184] the lack of any political representation both in Italy and in the European Parliament[185][186] (due to an unbalanced electoral constituency that still remains to this day,[187] Sardinia has not had its own MEP since 1994),[188] the nuclear power and waste (on which a referendum was proposed by a Sardist party,[189] being held in 2011[190]) and the ongoing process of depopulation and Italianization that would destroy the Sardinian indigenous culture.[191]

There is a separatist movement in Wallonia although secession of Flanders from Belgium seems more likely. There is also a movement for a union with France. Although the majority is Francophone, the Walloon movement includes the Allemanophones. There are various proposals, both within and outside the independentist movement, for what should happen to Brussels.[158][159]

Area shown in orange under control of Northern Cyprus

Officially, the island nation of Cyprus is part of the European Union, under the de jure sovereignty of the Republic of Cyprus. Turkish Cypriots are citizens of the Republic of Cyprus and thus of the European Union, and were entitled to vote in the 2004 European Parliament election (though only a few hundred registered). The EU's acquis communautaire is suspended indefinitely in the northern third of the island, which has remained outside the control of the Republic of Cyprus since the Turkish invasion of 1974. The Greek Cypriot community rejected the Annan Plan for the settlement of the Cyprus dispute in a referendum on 24 April 2004. Had the referendum been in favour of the settlement proposal, the island (excluding the British Sovereign Base Areas) would have joined the European Union as the United Cyprus Republic. The European Union's relations with the Turkish Cypriot Community are handled by the European Commission's Directorate-General for Enlargement.[192]

The European Council has recognised that following the UK withdrawal from the EU, if Northern Ireland were to be incorporated into the Republic of Ireland to form a united Ireland it would automatically rejoin the EU under Ireland's membership. This is consistent with the incorporation of East Germany into the Federal Republic of Germany as a single European Communities member state.[193][194]

A similar scenario has been envisioned with the unification of Moldova and Romania, which would incorporate the current territory of Moldova into Romania and thus into the EU.[195] About 44% of the Moldovans that were polled in 2021 supported such a scenario.[196]

Puerto Rico is an unincorporated territory of the United States. The reunification of the island with Spain, and its integration into the EU, as a Spanish autonomous community has been proposed.[197][198][199] There is a similar proposal for Cuba. However, unlike for Puerto Rico, it doesn't have political representation and is maintained in French associations.[200][201]

The Faroe Islands, a self-governing nation within the Kingdom of Denmark, is not part of the EU, as explicitly asserted by both Rome treaties.[202] The relations with the EU are governed by a Fisheries Agreement (1977) and a Free Trade Agreement (1991, revised 1998). The main reason for remaining outside the EU is disagreements about the Common Fisheries Policy,[203] which disfavours countries with large fish resources. Also, every member has to pay for the Common Agricultural Policy, which favours countries having much agriculture which the Faroe Islands does not. When Iceland was in membership negotiations around 2010, there was a hope of better conditions for fish-rich countries, but to no avail. The Common Fisheries Policy was introduced in 1970 for the very reason of getting access for the first EC members to waters of candidate countries, namely the United Kingdom, Ireland, and Denmark including the Faroe Islands.

Nevertheless, there are politicians, mainly in the right-wing Union Party (Sambandsflokkurin), led by their chairman Kaj Leo Johannesen, who would like to see the Faroes as a member of the EU. However, the chairman of the left-wing Republic (Tjóðveldi), Høgni Hoydal, has expressed concerns that if the Faroes were to join the EU as is, they might vanish inside the EU, comparing this with the situation of the Shetland Islands and Åland today, and wants the local government to solve the political situation between the Faroes and Denmark first.[204]

Greenland, a self-governing community that is part of the Kingdom of Denmark, entered the EC with Denmark in 1973, because it was not autonomous at that time. After the establishment of Greenland's home rule in 1979 (effective from 1980), it held a second referendum on membership. The result was (mainly because of the Common Fisheries Policy) to leave, so on 1 February 1985, Greenland left the EEC and EURATOM. Its status was changed to that of an Overseas Country.[205][206] Danish nationals residing in Greenland (i.e. all native population) are nonetheless fully European citizens; they are not, however, entitled to vote in European elections.

There has been some speculation as to whether Greenland may consider rejoining the European Union. On 4 January 2007 the Danish daily Jyllands-Posten quoted the former Danish minister for Greenland, Tom Høyem, as saying "I would not be surprised if Greenland again becomes a member of the EU... The EU needs the Arctic window and Greenland cannot alone manage the gigantic Arctic possibilities".[207] Greenland has a lot of natural resources, and Greenland has, especially during the 2000s commodities boom, contracted foreign private companies to exploit some of them, but the cost is considered too high, as Greenland is remote and severely lacks infrastructure which has to be built. After 2013 prices have declined so such efforts have stalled.

The Brexit debate has reignited talk about the EU in Greenland with calls for the island to join the Union again.[208]

The islands of Aruba and Curaçao, as well as Sint Maarten, are constituent countries of the Kingdom of the Netherlands, while Bonaire, Sint Eustatius and Saba are special Dutch municipalities. All are Overseas Countries and Territories (OCT) under Annex II of the EC treaty.[205] OCTs are considered to be "associated" with the EU and apply some portions of EU law. The islands are opting to become an Outermost Region (OMR) of the EU, a status in which the islands form a part of the European Union, though they benefit from derogations (exceptions) from some EU laws due to their geographical remoteness from mainland Europe. The islands are focusing on gaining the same status as the Azores, Madeira, the Canary Islands and the French overseas departments.

When Bonaire, Sint Eustatius, and Saba were established as Dutch public bodies after the dissolution of the Netherlands Antilles (which was an OCT) in 2010, their status within the EU was raised. Rather than change their status from an OCT to an outermost region, as their change in status within the Netherlands would imply, it was decided that their status would remain the same for at least five years. After those five years, their status would be reviewed.

If it was decided that one or all of the islands wish to integrate more with the EU then the Treaty of Lisbon provides for that following a unanimous decision from the European Council.[209] Former European Commissioner for Enlargement Danuta Hübner has said before the European Parliament that she does not expect many problems to occur with such a status change, as the population of the islands is only a few thousand people.

The territories of French Guiana, Guadeloupe, Martinique, Mayotte and Réunion are overseas departments of France and at the same time mono-departmental overseas regions. According to the EC treaty (article 299 2), all of these departments are outermost regions (OMR) of the EU—hence provisions of the EC treaty apply there while derogations are allowed. The status of the Overseas collectivity of Saint-Martin is also defined as OMR by the Treaty of Lisbon. New Caledonia and the overseas collectivities of French Polynesia, Saint-Barthelemy, Saint Pierre and Miquelon as well as Wallis and Futuna are Overseas Countries and Territories of the EU.[205]

New Caledonia is an overseas territory of France with its own unique status under the French Constitution, which is distinct from that of overseas departments and collectivities. It is defined as an "overseas country" under the 1998 Nouméa Accord, and enjoys a high degree of self-government.[210] Currently, in regard to the EU, it is one of the Overseas Countries and Territories (OCT).

As a result of the Nouméa Accord, New Caledonians voted in three consecutive independence referendums in 2018, 2020, and 2021. The referendums were to determine whether the territory would remain a part of the French Republic as a "sui generis collectivity", or whether it would become an independent state. The accords also specify a gradual devolution of powers to the local New Caledonian assembly. The results of all three referendums determined that New Caledonia would remain a part of the French Republic.