Spain, Portugal, France, Italy and Belgium all use the euro as their official currency, notes the European Commission. Slovenia, Germany and Austria are others. Lithuania, Latvia and Finland also use the euro.
The United Kingdom and Denmark opted out of using the euro when joining the European Union, notes the European Commission. In all, 19 countries use the euro as of 2015, representing 337.5 million people in the European Union. Some countries have not met the conditions required by the EU to adopt the euro. The euro's purpose is to provide a single currency to eliminate currency exchange expenses, facilitating international trade.