Beyond all reasonable doubt, black holes are commonly found in the nuclei of most normal galaxies. In recent years, dynamical measurements of hole masses have transformed the study of their functioning and evolution. In particular, relating their masses, as measured contemporaneously, to the properties of distant quasars can constrain models of the combined evolution of black holes and their host galaxies. It is suggested that black hole growth is radiation-dominated and demand-limited with an e-folding time of ~ 40 Myr and that most local black hole mass was assembled in AGN with redshifts, z > 2, whose counterparts are not directly observed today. Black hole binaries have additional features and observable consequences.