We review the most important findings on AGN physics and cosmological
evolution as obtained by extragalactic X-ray surveys and associated
multiwavelength observations. We briefly discuss the perspectives for future
enterprises and in particular the scientific case for an extremely deep (2-3
Ms) XMM survey.Comment: 5 pages, 4 figures, review talk at the conference: "XMM-Newton: the
next decade", updated to match version in pres