The Euro is the currencies of the countries member of the European Union which have adopted the Euro. The Euro was introduced on January 1st 2002 in 11 countries and gradually other countries have also adopted the Euro as shown in the map below:

The euro is the second most traded currency on the Forex. It is present in 39.10% of transactions in 2010. Its overall share in the number of transactions increases gradually each year but still far from the dollar and its hegemony. In 2004, the euro was present in 37.40% of transactions on Forex. The Euro is a currency of reference both in the foreign exchange market and in international trade. The euro is also the first currency in terms of banknotes in circulation.
The Euro is however considered as a currency risked. Investors buy the euro if they think the global economy is healthy. However, in times of crisis, the dollar appreciates against the euro. Indeed, the dollar is considered a safe haven.
The Euro (EUR) is controlled by the European Central Bank (ECB) which is responsible for making monetary policy decisions.