The European Coal and Steel Community and the European Economic Community, later known as the European Community (EC), were the forerunners of the European Union. The European Economic Community was founded in 1957 through the Treaty of Rome. Its main objective, as the name implies, was to promote economic integration among its member states. Since 1958, numerous European countries have joined the EC and its successor, the EU. This webpage presents a timeline of all the countries that have joined the EU since then. The EU enlargement policy will also be briefly covered on this page. The accession treaties and each phase of EC/EU enlargement will be examined in more detail on other webpages.
1952 and 1958: Belgium, France, Germany, Italy, Luxembourg and the Netherlands were the founding nations of the European Coal and Steel Community and the European Economic Community. The so-called Six laid the foundation for what became one of the largest internal markets in the world.
1973: In 1973 Denmark, Ireland and the United Kingdom joined the EC. Prior to the United Kingdom’s accession, the French government, under the leadership of Charles de Gaulle, had vetoed the British application in 1963 and 1967.
1981: The military junta in Greece had fallen in 1974. A few years later, in 1981, Greece joined the EC. This decision was controversial because the European Commission had warned that Greece was not ready for accession, as its industrial base was relatively weak compared to those of the other Member States. Helmut Schmidt, the former German Chancellor, was also critical of Greek membership in the EC. His main criticism concerned the inability of the Greek public administration to effectively tax its wealthier citizens. It was ultimately decided that Greece would be allowed to join the EC due to cultural and historical reasons.[1]
1984: In a consultative referendum held in 1982, the people of Greenland voted to leave the EC. Approximately 53% of the Greenlandic electorate voted in favor of leaving the EC. In 1984, Greenland officially left the EC.
1986: In 1986, Portugal and Spain joined the EC. More than a decade earlier, both countries were ruled by dictatorial regimes. These autocratic regimes in Portugal and Spain collapsed in 1974 and 1975, respectively.
1995: Austria, Finland and Sweden were the first European countries to join the newly founded European Union (EU) after the end of the Cold War. The EU was established in 1993 following the signing of the Maastricht Treaty the previous year.
2004: In 2004, the largest expansion of EU membership took place. The EU gained ten new Member States. These new Member States were Cyprus, Czechia, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.
2007: Bulgaria and Romania became members of the EU in 2007.
2013: Croatia is the newest Member State of the EU. Croatia joined the EU in 2013.
2020: In 2020, the United Kingdom left the European Union following the Brexit vote in 2016 and extensive negotiations. Before leaving the European Union, the United Kingdom had the most opt-outs of any EU member state, totalling four. These opt-outs meant it was not required to comply with certain treaties or legislation from the EU. For example, the United Kingdom was not obligated to adopt the euro as its currency and also had an opt-out for the Charter of Fundamental Rights of the European Union.
Since 2013, no new country has been admitted to the EU. Several countries have been granted candidate status by the EU. The following countries have received this status: Albania, Bosnia and Herzegovina, Georgia, Moldova, Montenegro, North Macedonia, Serbia, Türkiye and Ukraine.[2]
A country must go through three stages to become a Member State of the EU. The first stage requires that a potential Member State be granted candidate status by the EU. The second stage involves extensive negotiations that must take place before a country is ready to become a full-fledged member of the EU. During this stage, a country has to adopt and implement reforms to align with the judicial, administrative and economic policies of the EU. This includes changing national laws to comply with existing EU laws. The third stage begins after the negotiations and reforms have been completed. However, the third stage can only be completed if both parties (EU Member States and the candidate country) are satisfied with the progress made. To successfully complete all three stages, the candidate country must receive unanimous backing from all EU Member States. After all parties have signed the accession treaty, the candidate country becomes an acceding country. The acceding country will then become a Member State on the date agreed in the treaty once all parties have ratified the accession treaty.[3]
To successfully join the EU, a candidate country must meet the conditions outlined in the accession criteria, also known as the Copenhagen criteria. These criteria were established in 1993 during a European Council meeting in Copenhagen, Denmark. The criteria focus on three main areas. First, a candidate country must have a functioning market economy capable of operating competitively within the EU. Second, the country must adhere to the objectives of the EU and have the capacity to adopt European policies, rules and standards as defined by EU law. These objectives, rules, policies and standards are collectively referred to as the acquis communautaire of the EU. Lastly, candidate countries are required under the Copenhagen criteria to uphold the rule of law, human rights, democracy, and the protection of minorities within their own territories.[4]
To successfully join the EU, a candidate country must meet the conditions outlined in the accession criteria, also known as the Copenhagen criteria. These criteria were established in 1993 during a European Council meeting in Copenhagen, Denmark. The European Council defines the general political priorities and direction of the entire Union. The criteria focus on three main areas. First, a candidate country must have a functioning market economy capable of operating competitively within the EU. Second, the country must adhere to the objectives of the EU and have the capacity to adopt European policies, rules, and standards as defined by EU law. These objectives, rules, policies, and standards are collectively referred to as the acquis communautaire. Lastly, candidate countries are required under the Copenhagen criteria to uphold the rule of law, human rights, democracy, and the protection of minorities within their own territories.[4]
[1] James Angelos, “Why on earth is Greece in the EU?,” Politico, June 22, 2015, https://www.politico.eu/article/why-is-greece-in-the-eu-grexit/.
[2] Reuters, “Ten countries hope to join the European Union. Here is their formal status,” Reuters, October 30, 2024, https://www.reuters.com/world/europe/candidates-join-european-union-2024-10-30/.
[3] “Enlargement,” European Commission, accessed January 19, 2026, https://commission.europa.eu/topics/enlargement_en; “Steps towards joining,” European Commission, accessed January 19, 2026, https://enlargement.ec.europa.eu/enlargement-policy/steps-towards-joining_en.
[4] “Accession criteria (Copenhagen criteria),” EUR-Lex, accessed January 20, 2026, https://eur-lex.europa.eu/EN/legal-content/glossary/accession-criteria-copenhagen-criteria.html; “Acquis,” EUR-Lex, accessed January 20, 2026, https://eur-lex.europa.eu/EN/legal-content/glossary/acquis.html.