Enlargement of the European Union
Map source: Copyright European Union. The largest enlargement of the European Union occurred in 2004 with the accession of 10 new countries: Czech Republic, Estonia, Cyprus, Latvia, Lithuania, Hungary, Malta, Poland, Slovakia and Slovenia. Later, Romania and Bulgaria joined. Finally, Croatia was the latest country to accede to the European Union in 2013. Current candidate countries (meaning countries that are still negotiating membership or are waiting to begin negotiations) include the Former Yugoslav Republic of Macedonia, Iceland, Montenegro, Serbia, and Turkey.
last updated July 30, 2013

In 1993, the representatives of each European Union (EU) Member State met in Copenhagen for the European Council and there determined that "the countries in Central and Eastern Europe that so desire shall become members of the Union. Accession will take place as soon as a country is able to assume the obligations of membership by satisfying the economic and political conditions." The enlargement of the European Union, when new Member States enter, is known as the accession process.

A significant aspect of the accession process is the requirement that candidate countries adhere to all the policies and rules of the EU, known collectively as the acquis communautaire, and "ensure its effective implementation and enforcement through appropriate administrative structures."[1] The acquis derives from the founding treaties of the European Union and consists of 35 chapters. Each candidate country must state a position on each of the acquis chapters, which begins the negotiation process for membership.

The process of accession consists of three steps: becoming a candidate for membership, beginning formal membership negotiations, and joining the European Union. Negotiations between the EU and candidate countries cannot begin until a unanimous decision is reached by the EU on the framework or mandate for formal negotiations.[2]

The negotiations focus on the "terms under which the applicants will adopt, implement and enforce the acquis, and, notably, the granting of possible transitional arrangements which must be limited in scope and duration."[3] A further definition and description of EU law can be found on the website of the European Union.

In the Pre-Accession stage, candidate countries begin to align their legal and institutional framework with the European Union structure. This is conducted through the creation of partnerships between the European Union and each candidate country. Under the Accession Partnerships, the priority areas for the country are identified and negotiations begin about how the European Union will support efforts to reform the country's infrastructure. For example, the Instrument for Pre-accession assistance is a mechanism through which candidate countries can receive funding and support from the European Union during the accession process.[4] At the same time, the candidate country creates a National Program for the Adoption of the acquis, which is a detailed program and commitments of how the country will organize efforts to address the priority areas.

In 1993, the European Council established a set of criteria, known as the "Copenhagen Criteria" for countries seeking accession in the EU. The Copenhagen Criteria require:

  • Stability of institutions guaranteeing democracy, the rule of law, human rights and respect for and protection of minorities;
  • The existence of a functioning market economy, as well as the capacity to cope with competitive pressure and market forces within the Union; and
  • The ability to take on the obligations of membership, including adherence to the aims of political, economic and monetary union.

The Copenhagen Criteria and the acquis communautaire are the basis for accession negotiations between the European Union, represented by the Member States, and the candidate countries. The candidate countries establish a position on each of 35 negotiating chapters of the acquis , after which the negotiating positions must be approved unanimously by the Member States. Negotiation is carried out though bilateral Accession Conferences, held at the ministerial level between the Member States and candidate countries. The results of the negotiations are set forth in an Accession Treaty, which includes the conditions of entry, "the principles governing the incorporation of the new member, transitional measures and temporary exemptions, the transposition of the Community acquis, and rules on the temporary application of Community law." Both the European Council and Parliament must approve of the Accession Treaty, after which it is sent to the Member States and the Candidate State for ratification, which generally involves a national referendum. Once the treaty has been ratified, the candidate country becomes a Member State.

In 1998, the EU started accession negotiations with five Central and Eastern European applicant countries: Hungary, Poland, Estonia, the Czech Republic and Slovenia. In 1999, negotiations were opened with an additional five countries from the region: Romania, the Slovak Republic, Latvia, Lithuania and Bulgaria. In 2002, the European Commission recommended closing negotiations with the Czech Republic, Estonia, Hungary, Poland, Latvia, Lithuania, Slovenia, and the Slovak Republic. The Member States of the European Union and the candidates for membership agreed in Copenhagen, Denmark on 13 December 2002 on a package for the admission of these eight countries to the Union. The European Parliament voted to approve the accession of these eight countries (together with Cyprus and Malta) in April 2003 after which the current Member States and the accession countries signed the Accession Treaty in Athens, Greece on April 16 2003. These countries became European Union members on May 1, 2004 following favorable referendums on the accession in the accession countries and ratification of the treaty by current Member States and all of the accession countries.[5]

In January 2007, Bulgaria and Romania acceded to the European Union. On January 22, 2012, Croatians voted to accede in an EU referendum, allowing Croatia to become the 28th member of the European Union on July 1, 2013.[6]
The European Union Enlargement website contains an overview of the enlargement process, with information about each of the  countries that acceded to the European Union  in 2004, 2007, and 2013.


[1]“Questions and Answers about the Fifth Enlargement (Archived),” European Commission, accessed June 18, 2013, http://ec.europa.eu/enlargement/archives/questions_and_answers/1-10_en.htm.
[2]“Steps towards joining,” European Commission, accessed June 18, 2013,  http://ec.europa.eu/enlargement/policy/steps-towards-joining/index_en.htm.
[4]“Overview - Instrument for Pre-accession Assistance,” European Commission, accessed June 18, 2013, http://ec.europa.eu/enlargement/instruments/overview/index_en.htm.
[5]“History: 2000-2009,” European Union, accessed June 18, 2013, http://europa.eu/about-eu/eu-history/2000-2009/index_en.htm.
[6]“History: 2012,” European Union, accessed June 18, 2013, http://europa.eu/about-eu/eu-history/2010-today/2012/index_en.htm.