  This paper summarizes the observations which provide the best evidence for
the presence of black holes in active galactic nuclei. This includes: X-ray
variability; kinematical studies using optical emission lines as well as the
distribution of megamaser spots; and the shape of the Fe K$\alpha$ X-ray
emission line. It also presents the current status of our understanding of
jet-dominated active galaxies (blazars), and briefly reviews the currently
popular AGN ``Unification Schemes.''
