In which year did ten countries join the European Union?

On 1 May 2004 ten new countries with a combined population of almost 75 million joined the European Union (EU). This was the largest expansion of the EU, in terms of territory, number of states, and population.

The simultaneous accessions concerned the following countries (sometimes referred to as the "A10" countries): Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia. Seven of these were part of the former Eastern Bloc (of which three were from the former Soviet Union and four were and still are members of the Central European alliance Visegrád Group). Slovenia was a non-aligned country prior to the independence, and it was one of the former republics of Yugoslavia (together sometimes referred to as the "A8" countries), and the remaining two were Mediterranean islands and two Members of Commonwealth of Nations.