Single currency
The EU has not only a common currency supplementing the national currencies, but a single currency. Consequently, the Euro has replaced the former national currencies within the, so-called, Eurozone. Circulation of national currencies is forbidden.
The European Central Bank in Frankfurt, Germany, is responsible for the single currency.
Links
See also Common currency, Euroland, Economic and Monetary Union and Optimum currency area.
http://ec.europa.eu/economy_fi......_euro/index_en.htm?cs_mid=2946