The Euro officially replaced a series of former national currencies in Europe in 2002, making the Euro the second most largely traded currency in the world, second only to the U.S. dollar. While some countries, such as the United Kingdom or Denmark, did not switch to the new currency, 27 other countries have, as of 2011, decided to adopt the Euro.
In 2002, the Euro officially became the national currency of all countries participating in the European Economic and Monetary Union, or EMU, also sometimes called the Eurozone. During the first few months of 2002, European citizens and tourists in those countries were able to use both the old currency and the Euro at the same time. However, at the end of this transition period, the old currencies lost their transactional value and could only be exchanged against Euros by one of the participating countries' central banks.
In Western Europe, Portugal, Spain, France, Belgium, Ireland, The Netherlands, Italy, Greece, Germany, Luxembourg, Austria and Finland replaced their former national currencies with the Euro. The former currencies of those countries were, respectively, the Portuguese escudo, the Spanish peseta, the French franc, the Belgian franc, the Irish pound, the Dutch guilder, the Greek drachma, the Deutsche mark, the Luxembourg franc, the Austrian schilling and the Finnish mark.
The first Eastern European countries to join the Eurozone were Estonia, Lithuania, and Slovenia which all joined in 2004. Since then, Cyprus, Latvia, Malta and Slovakia have also adopted the single European currency. The former currencies of those Eastern European currencies were the Estonian kroon, the Lithuanian lita, the Slovenian tolar, the Cypriot pound, the Latvian lat, the Maltese lira and the Slovak koruna.
Monaco, San Marino and Vatican City
Monaco, San Marino and Vatican, while not members of the European Union or of the Eurozone, also decided to adopt the Euro for practical reasons due to their close proximity with countries using the new single currency. The former currency of Monaco was the Monégasque franc, while San Marino and Vatican used respectively the Sammarinese lira and the Vatican lira.