The euro is the single currency for the European Union (EU); an economic and political partnership between 28 member states. Since its introduction in 1999, 19 states within the EU have adopted the euro. A number of sovereign states outside of the EU have also adopted the euro. These include the Principality of Andorra, the Principality of Monaco and the Vatican City.
The euro is the second most traded currency on the global foreign exchange markets after the US dollar. It is also a major reserve currency of the world, meaning many central banks and financial institutions hold euros as reserves.