Hard X-ray Surveys: A census of Black Holes
New instruments capable of sensitive surveys at the energies >20 keV are making a complete census of active supermassive black holes. Only in the hard X-ray band can the effects of obscuration by the the accreting material in the host galaxy be ignored. Surveys in all other wavebands are distorted by missed AGN or confusion with other sources of activity (starburst galaxies). The wide field instruments on Swift/BAT and INTEGRAL are currently mapping all the active galactic nuclei in the local universe. Results from these surveys have already changed our understanding of AGN populations significantly and continuing improvements will define the current state and late evolution of AGN. Selected hard X-ray focusing optics missions (NuSTAR, NEXT, and Simbol-X) will soon extend this understanding to the peak of AGN activity. Combined with Chandra deep field observations of the early universe, a complete understanding of the growth and develop black holes is within our grasp.