The primary objective of the Nice Treaty is, according to its proponents, to prepare the EU to accept new members. Twelve states are currently negotiating for membership: Bulgaria, Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Romania, Slovakia and Slovenia. Turkey has applied to join but substantive negotiations have not yet begun.
Candidate countries must show that they have "achieved stability of institutions guaranteeing democracy, the rule of law, human rights and respect for and protection of minorities, the existence of a functioning market economy as well as the capacity to cope with competitive pressure and market forces within the Union".
They must also agree to adopt the acquis communautaire - almost 70,000 pages of laws and regulations governing everything in the EU from human rights to food standards. This body of rules is divided into 31 chapters - agriculture, energy, company law, transport, etc. Once the EU agrees with a candidate country on how the rules will be applied in a particular policy area, the relevant chapter is said to be provisionally closed. Some countries, for example, will be unable to fulfil all EU environmental standards immediately. They will seek permission to phase in new standards.
By the middle of this month, Estonia, Slovenia and Cyprus had closed 18 chapters, while Bulgaria had closed just six. Poland, with 40 million people, is the biggest candidate country. Malta, with only 378,000 people, is the smallest.
Most are much less prosperous than the present EU member-states. When Ireland joined the EEC in 1973, its GDP per head of population was 60 per cent of the EEC average. The candidate countries have an average income of only 34 per cent of the EU average. No date has yet been set for the admission of the first new member-states but the Commission president, Mr Romano Prodi, has expressed the hope that some at least will vote in the next European elections in 2004.
Some experts predict a "big bang" enlargement which would admit 10 countries at once - Bulgaria and Romania are lagging too far behind the rest to join at the same time. A more likely prospect is that between four and six countries will join in 2004 or 2005 and the others will wait a few years.
Although Poland is making slower progress in negotiations than some of its neighbours, its size and political importance make it almost certain to be part of the first group to join.