When stage three of Economic and Monetary Union (EMU) began, on 1 January 1999, three EU Member States (Denmark, Sweden and the United Kingdom) decided not to adopt the single currency.
On 1 May 2004, ten new Member States (Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, the Czech Republic, Slovakia and Slovenia) joined the European Union, followed by Bulgaria and Romania on 1 January 2007. Among these countries, have joined the euro area till now: Slovenia on 1 January 2007, Cyprus and Malta on 1 January 2008, Slovakia on 1 January 2009 and Estonia on 1 January 2011.
While Denmark and the United Kingdom, in accordance with the terms of the relevant protocols annexed to the Treaty, have a special status with the right reserved to participate in the euro afterwards, all the others member States have the status of Member State with a derogation (Article 122 of the EC Treaty).
EU membership implies that NCBs of the new Member States are integrated into the ESCB and their governors become full members of the General Council. Experts from these NCBs have full-member status in the meetings of the ESCB committees whenever they deal with matters that fall within the field of competence of the General Council.
In order to join the euro area, an EU Member State must demonstrate that it has met the convergence criteria laid down in the EC Treaty.