In order to join the EU, the would-be member state must submit an application for membership to the Council of the European Union, which will then ask the European Commission to assess the applicant's ability to meet the conditions of membership.
Once the Commission delivers a positive opinion, and the Council unanimously agrees a negotiating mandate, negotiations are formally opened between the candidate and all the member states.
The basis of the accession negotiations is the adoption and implementation of the acquis. This principle is now included in the Lisbon Treaty. The different areas for which reforms are needed in order to meet the accession conditions are called "chapters of the acquis".
The candidate countries are required to adapt their administrative and institutional infrastructures and to bring their national legislation in line with all EU legislation in the areas of the different chapters. These are reviewed during the screening of the acquis and are evaluated regularly up until the time each chapter is closed.
If successful, the negotiations lead to precise terms and conditions which are enshrined in an Accession Treaty that the would-be member states sign with the current member states.
10 of the countries which started negotiations in Athens on 16 April 2003 became member states on 1 May 2004. Romania and Bulgaria became members on 1 January 2007.
The accession treaties state that new member states have the same rights and obligations as the original member states. Some obligations, laid down in special protocols, only enter into force after accession. The accession treaties and acts of accession have to be adopted unanimously by the existing member states and by every new member state.
There have been referenda in each of the ten new member states, except for Cyprus, in order to allow national ratification of the accession treaty. No referendum was held in Romania and Bulgaria.
If a country fails to ratify, the number of votes and seats and the figures for qualified majority voting are changed proportionally or technically without new negotiations among all member states.
A legal base for such change is inserted in the accession acts.
Membership negotiations are at the moment going on with Croatia, Macedonia (FYROM) and Turkey.
The Lisbon Treaty includes a new Article 8 TEU concerning agreements with neighbouring countries opening the possibility for a special partnership agreement with Turkey.
Notes
When an accession treaty is adopted, it is ratified and sent to the Italian Republic, which collects and keeps all instruments of ratification. The accession criteria, or Copenhagen criteria, are the essential conditions all candidate countries must satisfy to become a member state .
Links
European Commission: Directorate General for Enlargement http://ec.europa.eu/enlargement/index_en.htm
Summaries of legislation: Enlargement http://europa.eu/scadplus/leg/en/s40000.htm