XXL is a survey using the XMM-Newton telescope to cover two regions of 25 deg2 each, with 10 ks observations. This gives a point source sensitivity of 5 x 10-15 erg s-1 cm-2  in the (0.5 - 2) keV band. With more than 6 Ms it is the largest XMM-Newton project approved to date.

600 new galaxy clusters with redshifts up to 2 will be used to constrain the dark energy equation of state.