Deep X-ray surveys using ROSAT, ASCA and BeppoSAX have resolved a significant fraction of the cosmic X-ray background (XRB) into discrete sources and optical identifications are demonstrating that the XRB is largely due to accretion onto massive black holes, integrated over cosmic time. The deep soft X-ray surveys have detected a larger surface density of AGN than in any other waveband and find significant evolution in the space density of high-luminosity AGN contrary to the pure luminosity evolution which was the standard assumption so far. Considerable uncertainties still exist for the evolution of low-luminosity AGN. These findings are consistent with the notion that most larger galaxies contain black holes many of which have been active in the past. Of particular interest in the context of this conference is the space density of high-redshift AGN, which is consistent with a constant value in the range2<z<5.X-ray surveys are therefore prone to yield valuable insight into the formation and accretion history of black holes in the early universe. However, the characteristic hard spectrum of the XRB can only be explained if most AGN spectra are heavily absorbed. Thus as much as 80–90&percent; of the light produced by accretion may be absorbed by gas and dust clouds, which according to recent models could reside in nuclear starburst regions that feed the AGN. This scenario has important consequences for the current attempts to understand black hole and galaxy formation and evolution: The absorbed AGN will suffer severe extinction and therefore, unlike classical QSOs, will not be prominent at optical wavelengths. If most of the accretion power is being absorbed by gas and dust, it will have to be reradiated in the FIR range and be redshifted into the sub-mm band. AGN could therefore contribute a substantial fraction to the recently discovered cosmic FIR/sub-mm background which has already partly been resolved by deep SCUBA surveys. The AGN light therefore needs to be taken into account when studying the star formation history in the early universe. ©1999 American Institute of Physics.