Flags of member countries in front of the European Parliament building in Brussels
(EPA/EMPICS)

What is the European Union?

The European Union (EU) is an agreement between European countries to act like one big state without borders.

It emerged out of the chaos at the end of the Second World War. In 1951, six countries, including Italy, France and West Germany, signed the Treaty of Paris. The idea was to stop any country being able to build enough weapons to start another war, by controlling the production of coal and steel. The UK didn't sign up until 1973, after a nationwide 'yes' vote to join what was then called the EEC.

In 1992, the Maastricht Treaty brought the EU much closer together and introduced the idea of a single currency – the euro. Last year saw a huge enlargement, with countries like Estonia, Latvia and Malta joining. Now, almost every country in Europe is a member. And nearly all of them use the euro as their currency.

The EU is based in Brussels, where it has a parliament of elected MPs and a European court. Although it's over there in Belgium, the EU has a huge effect on our lives here. It's about much more than just a question of whether we should keep the pound. Now, UK laws have to fit in with EU laws. You can work and live in any European country. And all the EU economies have become tied together, from the wealthiest to the poorest.