The euro is a tangible symbol of European integration: more than 350 million people use it every day, making it the second most-used currency worldwide. The benefits of the common currency are immediately obvious to anyone travelling abroad or shopping online on websites based in another EU country, where prices can be compared easily and exchange costs are avoided.
EU countries using the euro
Currently, the euro (€) is the official currency of 21 out of 27 EU countries which together constitute the eurozone, officially called the euro area.
Although all EU countries are part of the Economic and Monetary Union (EMU), only those who have met specific economic and legal criteria have replaced their national currencies with the euro.
In some cases, EU countries can negotiate an opt-out from any of the European Union legislation or treaties and agree to not participate in certain policy areas. Denmark has done this for the single currency and kept its own currency after joining the EU.
How countries join the euro area
To join the euro area, EU countries are required to fulfil the so-called 'convergence criteria'.
These binding economic and legal conditions were agreed in the Maastricht Treaty in 1992. All EU countries, except Denmark, are required to adopt the euro and join the euro area, once they are ready to fulfil them.
There is no timetable for joining the euro area, so EU countries can develop their own strategies for meeting the conditions for euro adoption.
The European Commission and the European Central Bank jointly decide whether the conditions are met for euro area candidate countries to adopt the euro.
After assessing the progress made against the convergence criteria, the two bodies publish their conclusions.
The ECOFIN Council ratifies the accession of a new country in consultation with the European Parliament and the European Council.
If favourable, the adoption process can begin.