  Over the last few years, the existence of mutual feedback effects between
accreting supermassive black holes powering AGN and star formation in their
host galaxies has become evident. This means that the formation and the
evolution of AGN and galaxies should be considered as one and the same problem.
As a consequence, the search for, and the characterization of the evolutive and
physical properties of AGN over a large redshift interval is a key topic of
present research in the field of observational cosmology. Significant advances
have been obtained in the last ten years thanks to the sizable number of
XMM-Newton and Chandra surveys, complemented by multiwavelength follow-up
programs. We will present some of the recent results and the ongoing efforts
(mostly from the COSMOS and CDFS surveys) aimed at obtaining a complete census
of accreting Black Holes in the Universe, and a characterization of the host
galaxies properties.
