Virtually since the original six countries (France, Germany, Italy, Belgium, Luxembourg and the Netherlands) started what is now the EU in 1957. The first enlargement, in 1973, brought in the UK, Ireland and Denmark. In 1981, Greece joined, and Spain and Portugal in 1986, Austria, Finland and Sweden became members in 1995. And on 1 May 2004 the membership rose to 25, with the accession of Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.

A country that wishes to join the EU submits an application for membership to the Council of the European Union, which asks the European Commission to assess the applicant's ability to meet the conditions of membership, and particularly compliance with the basic values of the EU: the Treaty on European Union states that "The Union is founded on 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". If 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 negotiations cover the entire EU acquis, chapter-by-chapter, to seek agreement on when and how the candidate will align its laws and practice with EU requirements. Compliance with commitments is closely monitored throughout the process, and negotiations on any chapter are closed – provisionally - only when all the Member States are satisfied with the candidate's progress. Definitive closure of negotiations occurs only at the end of the process, and the precise terms and conditions agreed are enshrined in an Accession Treaty. A candidate can become a member when the European Commission has delivered its positive opinion, when the European Parliament has given its assent, when the Accession Treaty has been approved by the Member States, when all Member States and the candidate countries have ratified the Accession Treaty and when all ratification instruments have been deposited in Rome.

Successful development of the EU is inevitably influenced by the successful development of its neighbouring countries, so the EU has always sought close political and trade relations with them. For aspiring members, it has also provided help in their preparations for negotiations and eventual accession, tailor-made for their particular needs. This has always included assisting them in fully understanding the EU rules and the obligations that must be accepted for membership, and in familiarising them with the way the EU functions.

In the current phase of enlargement, the EU also provides specific technical help and targeted financial aid for acceding countries, candidates and potential future members that are still dealing with the challenges of establishing political stability, democratic institutions, functioning market economies, and prosperity for all their citizens. Programmes such as PHARE (set up in 1989 to help the countries of central and eastern Europe that were emerging from communism), ISPA and Sapard (designed to support infrastructure, agriculture and rural development in the candidate countries), CARDS (specifically for the countries of the Western Balkans) and a specific programme for Turkey have delivered more than €100 billion for aspiring countries and new Member States over the last decade, and are still in operation. In addition, further funding has been agreed for new Member States to help complete their transition.

Now a comprehensive new instrument for all pre-accession financial aid is being finalised, to respond to the current needs of enlargement. This will come into effect in 2007, and will be the channel for assistance to Turkey and all Western Balkan countries, both candidates and potential candidates for membership. At the same time, and alongside its financial aid, the EU will continue to cooperate with all these countries in making the adjustments that will help prepare them for closer integration with the EU.