Enlargement of the eurozone

The enlargement of the eurozone is an ongoing process within the European Union (EU). All member states of the European Union, except Denmark and the United Kingdom which negotiated opt-outs from the provisions, are obliged to adopt the euro as their sole currency once they meet the criteria, which include: complying with the debt and deficit criteria outlined by the Stability and Growth Pact, keeping inflation and long-term governmental interest rates below certain reference values, stabilizing their currency's exchange rate versus the euro by participating in the European Exchange Rate Mechanism (ERM II), and ensuring that their national laws comply with the ECB statute, ESCB statute and of the Treaty on the Functioning of the European Union. The obligation for EU member states to adopt the euro was first outlined by the Maastricht Treaty of 1992, which became binding on all new member states by the terms of their treaties of accession.

As of 2016^[update], there are 19 EU member states in the eurozone, of which the first 11 (Austria, Belgium, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, Portugal and Spain) introduced the euro on 1 January 1999 when it was electronic only. Greece joined 1 January 2001, one year before the physical euro coins and notes replaced the old national currencies in the eurozone. Subsequently, the following seven countries also joined the eurozone on 1 January in the mentioned year: Slovenia (2007), Cyprus (2008), Malta (2008), Slovakia (2009), Estonia (2011), Latvia (2014) and Lithuania (2015).

Seven remaining states are on the enlargement agenda: Bulgaria, Croatia, Czech Republic, Hungary, Poland, Romania and Sweden. Denmark is not obliged to join, though should the country decide to do so it may join the eurozone with little difficulty as Denmark is already part of the ERM-II. The United Kingdom has opted to stay outside of the EMU, and currently has no intention of adopting the euro, rather it held a referendum on continuing to be a member of the EU at all, which resulted in a 52%-majority vote in favour of the UK's leaving the EU.

...
Wikipedia