On January 1, 1999 one of the largest steps toward European unification took place with the introduction of the euro as the official currency in eleven countries (Austria, Belgium, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, Portugal, and Spain).

Today, the euro is the world's most powerful currency, used by more than 320 million Europeans in twenty countries. The countries currently using the euro are:

Andorra, Austria, Belgium, Cyprus, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Malta, Monaco, Montenegro, Netherlands, Portugal, San Marino, Slovenia, Spain, Vatican City

On January 1, 2008, the two newest countries adopted the euro - Cyprus and Malta.

Not all 27 members of the European Union (EU) are part of the Eurozone, the name for the collection of EU countries that utilize the euro.

Notably, the United Kingdom, Denmark, and Sweden have thus far decided not to convert to the euro. Other new EU member countries are working toward becoming part of the Eurozone. Monaco, San Marino, and the Vatican City are not EU members but do officially use the euro as their currencies, about.com reports.