The Enlargement of the Union

On 1 July 2013, Croatia became the 28th (now 27th) Member State of the European Union. Since then, no other countries have joined the EU, and the UK left the EU on 31 January 2020. Accession negotiations and chapters have been opened with Montenegro, Serbia and Türkiye. Albania and North Macedonia opened accession negotiations in July 2022. In December 2022, Bosnia and Herzegovina obtained candidate country status and Kosovo submitted its application for EU membership. In June 2022, the EU granted candidate country status to Ukraine and Moldova. On 8 November 2023, the Commission recommended that the Council open accession negotiations with Moldova and Ukraine (5.5.6).

Legal basis

  • Article 49 of the Treaty on European Union (TEU) establishes which states may apply;
  • Article 2 TEU describes the EU’s founding values.


The EU’s enlargement policy aims to unite European countries in a common political and economic project. Guided by the Union’s values and subject to strict conditions, enlargement has proved to be one of the most successful tools in promoting political, economic and social reforms, and in consolidating peace, stability and democracy across the continent. Enlargement policy also enhances the EU’s presence on the global stage.


A. Conditions for accession

Any European state may apply to become a member of the Union if it respects its common values and is committed to promoting them (Article 49 TEU). The Copenhagen criteria, established by the European Council in 1993 in Copenhagen, are essential in any candidate or potential candidate country’s EU integration process. They include:

  • The stability of institutions guaranteeing democracy, the rule of law, human rights and respect for and protection of minorities;
  • A functioning market economy and the ability to cope with competitive pressure and market forces within the EU;
  • The ability to take on the obligations of membership, including by adhering to the aims of political, economic and monetary union, and adopting the common rules, standards and policies that make up the body of EU law (the acquis communautaire).

In December 2006, the European Council agreed on a ‘renewed consensus on enlargement’, based on ‘consolidation, conditionality and communication’ and on the EU’s capacity to integrate new members.

B. The EU’s integration capacity: institutional arrangements

Successive enlargements formed a substantial part of the institutional negotiations that led to the adoption of the Treaty of Lisbon. The EU had to adapt its institutions and decision-making processes to the arrival of new Member States and ensure that enlargement would not come at the expense of efficient, accountable policymaking. The Treaty of Lisbon introduced profound changes to the composition and work of the main EU institutions. Some of these changes reflected the need for a sustainable set of rules that do not require new amendments with every new enlargement.

C. Process

A country that wishes to join the EU addresses its application to the Council, which asks the Commission to submit an opinion. Parliament is notified of this application. If the Commission’s opinion is favourable, the European Council may decide – by unanimity – to grant the country candidate status. Following a recommendation by the Commission, the Council decides – again by unanimity – whether negotiations should be opened. The sum of EU legislation (the acquis communautaire) is divided into more than 30 policy chapters. Before actual negotiations start, the Commission delivers a ‘screening’ report for each chapter. On the basis of the Commission’s recommendation, the Council decides by unanimity whether or not to open more negotiation chapters or clusters of chapters. Whenever progress is judged satisfactory, the Commission may recommend ‘provisionally closing’ a chapter or cluster of chapters. The Council again decides by unanimity, taking into account the overall progress in the area of the rule of law. When negotiations on all the chapters or clusters of chapters are completed, the terms and conditions – including possible safeguard clauses and transitional arrangements – are incorporated into an accession treaty between the Member States and the acceding country. Only after Parliament’s consent and the Council’s unanimous approval can the accession treaty be signed. It is then submitted by all contracting states for ratification, in accordance with their constitutional requirements (i.e. ratification by parliament or referendum).

Past enlargements

Country Member since Particularities
The Netherlands
1958 Original signatories to the 1957 Treaty of Rome.
United Kingdom[1]
Greece 1981 Greece’s accession consolidated democracy in the country.
1986 This enlargement consolidated democracy in Portugal and Spain.
2004 Intended to reunite the continent after the fall of the Berlin Wall and the collapse of the Soviet Union, this enlargement was launched by the European Council meeting of December 1997. Negotiations were conducted separately with each country, based on a single negotiating framework.
2007 The pace of reform in Bulgaria and Romania did not allow these countries to join in 2004. A ‘cooperation and verification mechanism’ in key areas – judicial reform, the fight against corruption and the fight against organised crime (the latter applying only to Bulgaria) – was put in place to monitor progress after accession.
Croatia 2013 The accession negotiations with Croatia were subject to the stricter conditionality established in December 2006 by the European Council’s ‘renewed consensus on enlargement’.

A. Western Balkans

Relations with the Western Balkans fall within the framework of the Stabilisation and Association Process, launched in 1999. It is based on bilateral stabilisation and association agreements.

Croatia’s accession to the EU on 1 July 2013 constitutes a significant incentive for other countries in the region. Building on the experience with Croatia, the Commission proposed further improvements to its negotiating approach in its 2011-2012 ‘Enlargement Strategy’, including a stronger emphasis on rule of law issues. This means that negotiating chapters on judicial reform and fundamental rights (chapter 23) and on justice, freedom and security (chapter 24) are opened at an early stage in all future negotiations and that they are the last to be closed. This approach was reaffirmed and reinforced in the Commission communication of 5 February 2020 entitled ‘Enhancing the accession process – A credible EU perspective for the Western Balkans’, which introduced a revised methodology for enlargement to the Western Balkans. It is also part and parcel of the Economic and Investment Plan for the Western Balkans, which was published as part of the Commission’s 2020 enlargement package. On 8 November 2023, the Commission adopted a new EUR 6 billion growth plan for the Western Balkans, based on four pillars and covering the 2024-2027 period. The plan intends to bring some of the benefits of EU membership to the region in advance of accession, with strong ex ante conditionality for payments.

Russia’s war of aggression against Ukraine and the EU’s decision of June 2022 to grant candidate country status to Ukraine and Moldova have also triggered an ongoing debate on the acceleration of the EU integration process of the Western Balkan candidate and potential candidate countries.

To date, all 33 screened negotiating chapters with Montenegro have been opened, but only three have been provisionally closed. Serbia has opened 22 out of 35 negotiating chapters, of which two have been provisionally closed. Despite the considerable number of opened chapters, EU integration-related reforms in both countries have largely stalled over the past years.

In March 2020, the Council finally gave the green light to open accession negotiations with Albania and North Macedonia (with a set of conditions for Albania). In July 2020, the Commission presented the draft negotiating frameworks – the first to take into account the ‘revised methodology for enlargement to the Western Balkans’ – to the Member States. Accession negotiations with both countries were formally opened in July 2022 following long delays mainly stemming from issues between North Macedonia and Bulgaria related to identity, language and history.

The Stabilisation and Association Agreement between the EU and Bosnia and Herzegovina (BiH) entered into force on 1 June2015. In February 2016, BiH submitted its membership application. In its opinion of May 2019, the Commission listed 14 key priorities that BiH must fulfil in order to open accession negotiations. Despite its failure to deliver on most of these priorities, BiH was granted candidate country status in December 2022. On 8 November 2023, the Commission recommended opening EU accession negotiations with BiH ‘once the necessary degree of compliance with the membership criteria is achieved’.

The Stabilisation and Association Agreement between the EU and Kosovo entered into force on 1 April 2016. In December 2022, Kosovo applied for EU membership. Following a decisive vote in Parliament in April 2023, Kosovo will benefit from visa-free travel to the Schengen area by January 2024 at the latest. Kosovo is also conducting an EU-facilitated dialogue with Serbia that should lead to a legally binding comprehensive agreement on the normalisation of their relations. Both Kosovo and Serbia have yet to start implementing their obligations, stemming from a revamped agreement of early 2023 to rekindle the stalled dialogue.

B. Türkiye

Turkey applied for EU membership in 1987 and was declared a candidate country in 1999. Negotiations were opened in October 2005. Eight chapters are blocked, and no chapter will be provisionally closed until Türkiye applies the ‘Additional Protocol to the Ankara Association Agreement’ to Cyprus. Opening other chapters has been opposed by individual Member States. After a standstill of more than three years, a new negotiating chapter was opened in November 2013. Another was opened in December 2015. On 18 March 2016, Turkey and the EU reaffirmed their commitment to implementing their joint action plan to stem the flow of irregular migrants to the EU and to re-energise the accession process. This led to the opening of an additional chapter in June 2016, bringing the total number of opened chapters to 16 out of 35, of which one has been provisionally closed. However, in the light of the dramatic deterioration of the rule of law in Türkiye, in particular in the aftermath of the July 2016 attempted coup, the accession process with Türkiye is de facto frozen. EU-Türkiye relations have further deteriorated as a result of Türkiye’s foreign policy choices, its unilateral actions in the Eastern Mediterranean and its promotion of a ‘two-states-on-one-island’ solution to the Cyprus issue.

Role of the European Parliament

Under Article 49 TEU, Parliament must give its consent to any new accession to the EU. It also has a significant say over the financial aspects of accession: its budgetary powers give it direct influence over the amounts allocated to the Instrument for Pre-accession Assistance.

Parliament’s Committee on Foreign Affairs appoints standing rapporteurs for all candidate and potential candidate countries. Parliament expresses its positions on enlargement in the form of annual resolutions responding to the Commission’s latest annual ‘country reports’. On 23 November 2022, it adopted recommendations on a new EU strategy for enlargement. Parliament also maintains bilateral relations with the parliaments of all enlargement countries through its delegations, which regularly discuss with their counterparts issues that are relevant to their respective EU integration paths. It has observed elections in all enlargement countries except Türkiye, which has yet to invite Parliament to do so.


[1]The United Kingdom left the EU on 31 January 2020 (at 11 pm GMT).

André De Munter