The forerunner to the European Union was formed by six countries in 1952 and now has 28 members with a combined population of more than 500 million people.
It is set to expand even further, with several countries being considered for membership.
The European Union has its roots in the 1951 agreement by France, Germany and four other countries to pool coal and steel supplies, with the aim of ending "age-old rivalries".
In 1993 EU leaders adopted the so-called Copenhagen criteria setting standards for democracy, human rights, the rule of law, minority protection and civilian control over the military that all candidate states must meet to become members.
The maps below show how the economic bloc has grown over the years.