The EU agreed to begin proceedings to admit a large number of new member states from Eastern and Central Europe in 1997, and the accession process began in 1998.
Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, the Slovak Republic, and Slovenia joined the EU on May 1st 2004.
Whilst the EU had successfully enlarged on four previous occasions (1973, 1981, 1986 and 1995), it had never before taken on so many new members at once. The ten states that joined in 2004 added 105 million to the population of the EU, and increased its geographical size by 34 per cent.
Bulgaria and Romania joined in 2007, bringing the total number of member states to 27.
To qualify for EU membership, a state must meet the 'Copenhagen criteria'.
1. To be a stable democracy, respecting human rights, the rule of law, and the protection of minorities.
2. To have a functioning market economy.
3. To adopt the common rules, standards and policies that make up the body of EU law – that is, to incorporate the acquis communautaire into domestic law.