ESF is not a funding agency. It can best be described as a networking organisation for its member organisations, who themselves are often funding agencies. ESF’s funding is provided by its member organisations.
Apparently the ESF was set up in 1974 and currently has 79 members in 30 European countries, so quite a sprawling network.
I was curious how many staff the organisation employed and what it’s budget was – mysteriously neither seem currently available, just figures from 2006!
Update (see comment below): ESF have kindly informed me that the ESF budget was 58 million euro in 2009 (including 30 million for COST:European Cooperation in Science and Technology), and ESF employed the equivalent of 170 full time staff, including COST employees.
The ESF is to be contrasted with the European Research Council which does provide funding.
Interestingly the President of the Governing Council for ESF 2010 is Professor Ian Halliday, who I recollect from my days at Imperial College when I was doing my PhD there (in theoretical high-energy physics), small world (as always).