A club of European countries. Initially a six-country trade area established by the 1957 Treaty of Rome and known as the European Economic Community, it has become an increasingly political union. In 1999 a single currency, the Euro, was launched in 11 of the then 15 member countries. Viewed as a single entity, the EU has a bigger economy than the United States. In 2002, a further 10 countries were invited to join the EU in 2004, increasing its membership to 25 countries, with more countries likely to follow later.