The European Commission is more than simply a civil service for the European Union - it is the only body that can propose legislation.
It is sometimes seen as the driving force behind European integration.
The commission is made up of 27 commissioners - the president and 26 others, each with responsibility for a policy area, such as agriculture or enlargement. A number of directorates general cover similar policy areas.
Commissioners are appointed by the member states, and are usually senior politicians. However, their job is to act in the general European interest, not to advance the interests of their own country.
For the time being the number of commissioners will remain at 27, but this will change in 2014, under the Lisbon Treaty.
From 2014 only two-thirds of member states will have a commissioner at any one time - so all will have a commissioner for 10 years out of every 15.