The basic principle for ESO's participation in the EU Framework Programmes is that the EU contracts cover non-core activities of ESO and/or are applications in partnerships with national institutes where ESO's participation will strengthen both the potential outcome of the project and its chances of leading to a contract. Furthermore, the fact that several consortia include institutes in ESO non-member states strengthens ESO's position in the whole scientific community regardless the membership.

The projects funded (or co-funded) by the EC are important for ESO under the perspective of the ERA and the Lisbon Process, but also to some extent to support further the integration of the European astronomical community. Many of the projects historically evolved in areas, which the ESO Convention did not establish as main fields of activity, but which have grown in importance with time. These activities are also very often implemented in partnership with national organisations and/or other European organisations, which for ESO in terms of legal solutions can most easily be implemented through EC contracts.

A main characteristic of the EC funded/co-funded projects is that ESO provides the expertise, and where appropriate the facilities, whereas the EC provides (the bulk) of the funding.

Typical fields where the EC projects could add to the activities of ESO are high-profile educational activities, some technology development activities or support for scientific networks that require Europe-wide participation. Since the launch of the 7th Framework Programme, ESO also cooperates with the EC in the field of the future large European infrastructures.