with 7.3 percent of the world's population, more than 500 million people.

It generates around 24 percent of global nominal gross domestic product.

In 2003, there were 15 member states.

Today, there are 28.

The Eurozone is a monetary union, member states have adopted the euro

as their common currency and sole legal tender.

Those countries within the Schengen Area, have abolished passports

and any type of border control at their mutual borders.

The European Free Trade Association operates in parallel with the EU,

and all member states participate in the EU single market.

The European Economic Area, allows free movement of

persons, goods, services and capital within the internal market of the EU.

The UK, is already less integrated into Europe than most EU member states.

Then there are those nations that are outside of those groups

but part of the Council of Europe,

which unlike the EU, cannot make binding laws.

And separate agreement exists between the EU with Monaco,

San Marino, and the Vatican to mint euros.