Although we now take it for granted, the 'single market' (sometimes also called the 'internal market') is one of the EU’s greatest achievements. Instead of being obstructed by national borders and barriers, people, goods, services and money move around the EU as freely as they do within a single country.
We travel at will across the EU’s internal frontiers for business and pleasure or, if we choose, we can stay at home and enjoy a vast array of products from all over Europe.
Most households in Europe are free to choose their electricity supplier.
To create this unified market, hundreds of technical, legal and bureaucratic barriers that stifled free trade and free movement between the EU's member countries were abolished in a series of reforms, culminating in 1993.
According to the Commission, these reforms generated 2.75 million extra jobs and growth of 1.85% between 1992 and 2009.
Free to do business across the entire economic bloc, companies have expanded their operations, with the resultant competition both bringing down prices and increasing consumer choice.
Phone calls in Europe cost a fraction of what they did 10 years ago, many air fares have fallen significantly and new routes have opened. Many homes and businesses are now able to choose who supplies them with electricity and gas.
At the same time, the EU works to ensure these greater freedoms don't undermine fairness, consumer protection or environmental sustainability – aided by Europe's various competition and regulatory authorities.
European firms selling in the EU have unrestricted access to nearly 500 million consumers – giving them a solid basis for staying competitive in the world economy. Not to mention the attraction of such a vast unified market for foreign investors.
And economic integration can be a valuable defence against periodic recessions, allowing EU countries to continue trading with one another rather than resorting to narrow protectionist measures that would worsen the crisis.
Skilled professionals can work anywhere in the EU.
Integration still has some way to go, however – there are many areas of untapped potential.
For a start, the fragmented nature of national tax systems puts a brake on market integration and efficiency.
And the services sector has opened up more slowly than markets for goods, despite a major new law in 2006 enabling companies to offer a range of cross-border services from their home base.
Delays have affected financial services and transportation, where separate national markets still exist.
On financial services, the EU is seeking to avoid a repeat of the 2009 crisis by building a safer and stronger financial sector, through measures including supervising financial institutions, regulating complex financial products and requiring banks to hold more capital.
Most EU countries have agreed to remove passport checks at their borders with fellow EU countries, when travelling by land (air travellers are still required to show some identity).
The exceptions to this are 5 countries that retain national border controls: Cyprus, Ireland, the UK, Bulgaria and Romania.
However, this is in return for tighter controls at the EU’s external borders – to prevent criminals of all sorts taking advantage of the system, supplemented by: