The EU is a unique economic and political partnership between 28 European countries that together cover much of the continent.
It was created in the aftermath of the Second World War. The first steps were to foster economic cooperation: the idea being that countries who trade with one another become economically interdependent and so more likely to avoid conflict.
In 1951, six countries founded the European Coal and Steel Community, and later, in 1957, the European Economic Community and the European Atomic Energy Community:
Belgium
Germany
France
Italy
Luxembourg
The Netherlands
A further 22 countries have since joined the EU, including a historic expansion in 2004 marking the re-unification of Europe after decades of division.