The EU is a political and economic union of 28 member states, founded in 1993.
The origins of the union lie in the European Economic Community (EEC), a group formed in postwar Europe that originally consisted of Belgium, France, Italy, Luxembourg, the Netherlands and West Germany. Britain joined the EEC in 1973.
In 1985, the Schengen Agreement paved the way for the creation of open borders without passport controls.
Okay: but what does the EU actually do?
The EU operates a single market which allows the free movement of people, goods, services and capital between member states.
This means that people can move between EU countries freely. Any product legally manufactured in one country can be sold in another without incurring duties. Taxes are standardised. Firms that provide things like medicine and tourism services can operate across borders.
The EU has helped ensure the cost of air travel, overseas phone calls and internet services are low – but some believe its regulations are too restrictive.
Which countries are in the EU?
There are 28 countries in the EU. They are:
Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus,Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden and, at the time of writing, the UK.
The UK entered the EEC in 1973. It was a founder member of the EU. On June 23, 2016, UK citizens voted to leave the union.