Gone are the days of exchanging currency whenever you cross a border in Europe. In 2002 the euro replaces national currency in 12 countries - first as a virtual currency for monetary transactions and then in hard cash.
Although the euro was introduced as a common currency for 12 countries in 2002, plans for the monetary unit are actually much older. The first step on the road to a common European currency was undertaken in 1979 when the European Currency System was established. In 1988 plans were drafted for the European Economic and Currency Union. In 1999 the euro was introduced as a monetary unit for all paper transactions. It wasn't until three years later that the euro became a hard currency in cash and coins.
The number of countries introducing the euro has expanded from the original 12. By 2011 17 countries had introduced the common currency. In Andorra, Montenegro and Kosovo, the euro is the only currency, even though the countries are not formally members of the euro zone. There are also several European Union members who have resisted joining the monetary union: the UK is the most prominent of these.