In May 2004, ten new countries joined the European Union (EU). These are the Baltic states of Estonia, Latvia and Lithuania; the ‘Visegrad’ countries of Poland, Hungary, the Czech Republic and Slovakia; the Mediterranean islands of Malta and Cyprus; and the only Balkan country, Slovenia. Romania and Bulgaria will follow in 2007 if they reform fast enough. The social, economic and spatial impact of the EU enlargement is considerable both for the new members and the Union as a whole. As in any other major transformation, the enlargement of the EU has led to strains and challenges as well as opportunities and rewards.