How Power Works · Institutions

How EU Enlargement Actually Works

Joining the European Union requires unanimous political decisions at key stages, extensive legal alignment and eventual ratification of an accession treaty by every member state and the candidate.

State & Power Explainer · Updated 2026-09-22 · 7 min read

Power map

From application to EU membership

01European country applies for membership

02Member states agree candidate status and negotiating framework

03Candidate negotiates and implements the acquis

04Accession treaty is agreed

05All member states and the candidate ratify the treaty

Membership is a political and legal process

Article 49 of the Treaty on European Union provides the treaty basis for European states seeking membership. Applicants must respect the Union's values and meet political, economic and institutional conditions associated with accession.

The European Commission assesses progress, but member states retain decisive political power at key stages.

Negotiations are divided across the EU rulebook

Candidates are expected to align domestic law and institutions with the EU acquis. Negotiations examine clusters and chapters of that body of law, with benchmarks used to assess readiness.

Opening negotiations is therefore not the same as receiving a guaranteed date of membership. Implementation and political agreement can take years.

Existing members retain powerful veto points

Key enlargement decisions require agreement among member states, and the final accession treaty must be signed and ratified according to the constitutional requirements of the parties.

That gives every existing member significant leverage even after a candidate has completed extensive technical reforms.