  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 $\sim40$ 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.
