At present there are 17 countries in the Eurozone (ie, using the Euro as a currency.) You can see a list here with details about when the countries joined. The euro is under the control of the European Central Bank. The major countries in the Eurozone are France and Germany, who were the main force behind the new currency when it was launched in 1999 (though it didn't become the only currency until 2002.)

At the moment there are questions about the future of the Eurozone, and especially about whether Greece will be able to stay in the single currency, as it has severe economic problems which some people think would be eased if they had their own currency and were able to devalue. However, Greece has been lent a huge sum of money to shore up its economy and the euro generally is starting to rise again.

There are also another 10 European Union states which are not in the Eurozone, but there is also the possibility that some of these could opt to join the euro in future. Meanwhile new states are applying for EU membership - Serbia is the most recent - so figures both for the EU and the Eurozone are likely to change.