According to Article 49 of the Treaty on European Union, any European country may apply for membership if it respects the principles of liberty, democracy, respect for human rights and fundamental freedoms, and the rule of law, principles which are common to the Member States' (Article 6.1 TEU). Accession, however, can only follow if the given European country fulfils all criteria of accession which were fixed by the European Council in Copenhagen in 1993 and reinforced by the European Council in Madrid in 1995. These criteria are:
- political: stable institutions guaranteeing democracy, the rule of law, human rights and respect for protection of minorities;
- economic: a functioning market economy and the capacity to cope with competition and market forces in the EU;
- the capacity to take on the obligations of membership, including adherence to the objectives of political, economic and monetary union;
- adoption of the acquis communautaire (the entire European legislation) and its effective implementation through appropriate administrative and judicial structures.
In addition, the EU must be able to absorb new members, so it reserves the right to decide when it will be ready to accept them.