Accession to the European Union: Criteria, Procedure, and Practice
Article 49 TEU governs the accession of new Member States to the European Union. The provision establishes that any European state which respects the values referred to in Article 2 TEU and is committed to promoting them may apply to become a member of the Union. Accession is the most consequential decision the Union can take, extending the scope of the EU legal order to new territories and populations. The accession procedure has been refined through successive enlargement rounds, developing a sophisticated framework of political conditions, legal alignment, and institutional preparation.
The Copenhagen Criteria
The Copenhagen criteria, established by the European Council in 1993, set out the conditions for membership. Political criteria require stable institutions guaranteeing democracy, the rule of law, human rights, and respect for and protection of minorities. Economic criteria require a functioning market economy and the capacity to cope with competitive pressure and market forces within the Union. Acquis criteria require the ability to take on the obligations of membership, including adherence to the aims of political, economic, and monetary union.
The Copenhagen criteria have been elaborated through subsequent European Council conclusions and Commission assessments. The political criteria have been given particular emphasis in the Western Balkans enlargement process, with the European Council adding requirements for cooperation with the International Criminal Tribunal for the former Yugoslavia and the resolution of bilateral disputes through good neighbourly relations. The rule of law, judicial reform, and the fight against corruption have become central to the accession assessment framework.
The Accession Procedure
Article 49 TEU establishes a multi-stage accession procedure. The application stage begins with the applicant state submitting its application to the Council. The Council consults the Commission and obtains the consent of the European Parliament, which acts by a majority of its component members. The European Council must confirm that the applicant meets the Copenhagen criteria before the accession process can formally begin.
The negotiation stage involves bilateral intergovernmental conferences between the Union and the applicant. The acquis is divided into 35 negotiating chapters covering all areas of EU law. Negotiations proceed on the basis of the principle that nothing is agreed until everything is agreed. Each chapter must be opened and closed by unanimous agreement of the Member States. The Commission monitors the applicant’s progress and reports to the Council. Negotiations may be suspended if the applicant seriously breaches EU values, as occurred with Turkey following the 2016 attempted coup.
The accession treaty stage follows the conclusion of negotiations. The accession treaty is signed by all Member States and the applicant state, then ratified by all signatories in accordance with their constitutional requirements. The treaty sets the date of accession and may provide for transitional arrangements, safeguard clauses, and institutional adjustments. The treaty must be approved by the European Parliament by a majority of its component members and by the Council acting unanimously.
Recent and Current Accession Processes
The 2004 enlargement was the largest in EU history, admitting ten new Member States: Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia. The 2004 enlargement followed the post-Cold War political transformation of Central and Eastern Europe and demonstrated the EU’s transformative power as a force for democratisation and economic modernisation. The enlargement was preceded by a comprehensive pre-accession strategy, including the Europe Agreements, the Accession Partnerships, and extensive financial assistance through the PHARE programme.
Subsequent enlargements admitted Bulgaria and Romania in 2007, Croatia in 2013. The accession of Bulgaria and Romania was subject to continued monitoring through the Cooperation and Verification Mechanism, which assessed progress in judicial reform, the fight against corruption, and (for Bulgaria) organised crime. The mechanism demonstrated the EU’s capacity to maintain post-accession conditionality. Croatia’s accession reflected the stabilisation and association process for the Western Balkans.
Current candidate countries include Albania, Bosnia and Herzegovina, Moldova, Montenegro, North Macedonia, Serbia, Turkey, and Ukraine. Georgia was granted candidate status in December 2023. Montenegro and Serbia have opened accession negotiations, while Albania and North Macedonia opened negotiations in 2022. The enlargement process has slowed due to reform fatigue in candidate countries, enlargement fatigue in Member States, and the EU’s absorption capacity. The European Council has emphasised the importance of rigorous conditionality, merit-based assessment, and the reversibility of progress in negotiations.
Accession and the EU Legal Order
Accession entails full acceptance of the acquis communautaire and the constitutional principles of the EU. Acceding states must accept the entire body of existing EU law, including Treaty provisions, secondary legislation, CJEU case law, and international agreements. Derogations and transitional periods may be negotiated for specific sectors, but opt-outs from core constitutional principles are not permitted. The principle of sincere cooperation under Article 4(3) TEU requires acceding states to take all appropriate measures to ensure fulfilment of the obligations arising out of the Treaties.
The legal effects of accession operate from the date specified in the accession treaty. From that date, EU law applies in the acceding state with full effect, including the direct effect and supremacy of EU law. The CJEU has jurisdiction over the interpretation and application of EU law in the acceding state from the date of accession. Pre-accession commitments and obligations, including the alignment of national legislation with the acquis, become legally binding and enforceable through infringement proceedings.
The European Perspective and Enlargement Strategy
The EU has developed the concept of a European perspective as the promise of eventual membership for European states that meet the criteria. The European perspective is distinct from a formal candidate status and provides a political horizon for reform. The Thessaloniki Agenda (2003) established the European perspective for the Western Balkans, later reaffirmed by successive European Council conclusions.
The enlargement strategy has evolved to emphasise fundamentals first: rule of law, economic governance, and public administration reform are addressed early in the negotiation process. The revised enlargement methodology, adopted in 2020, introduces stronger incentives, more predictable timelines, and greater political oversight. The methodology clusters negotiating chapters and links progress across them, preventing backsliding and rewarding sustained reform. Accession remains the most powerful instrument of the EU’s external influence and a central dimension of the Union’s geopolitical identity.