As I write the euro is the official currency of 19 of the current 28 member states of the European Union and also some of the territories of the Union. This group of states is known as the eurozone or euro area. The euro is the second largest and second most traded currency in the foreign exchange market after the United States dollar. The gradual introduction of the currency began at midnight on the 1st of January 1999, when the national currencies of participating countries in the eurozone ceased to exist independently.
There are many collectors of the various coin issues from different countries within the EU. And also many who are interested in the stamps released featuring the coinage.
The 10th anniversary of the currency was commemorated with stamps in 2009 by many of the EU member countries, some of which are shown below. For more see freestampcatalogue.com.