Report by the ESA-ESO Working Group on Fundamental Cosmology Abstract In September 2003, the executives of ESO and ESA agreed to establish a number of working groups to explore possible synergies between these two major European astronomical institutions on key scientific issues. The first two working group reports (on Extrasolar Planets and the HerschelнALMA Synergies) were released in 2005 and 2006, and this third report covers the area of Fundamental Cosmology. The Working Group's mandate was to