Massive Black Holes: Evidence, Demographics and Cosmic Evolution
  The article summarizes the observational evidence for the existence of
massive black holes, as well as the current knowledge about their abundance,
their mass and spin distributions, and their cosmic evolution within and
together with their galactic hosts. We finish with a discussion of how massive
black holes may in the future serve as laboratories for testing the theory of
gravitation in the extreme curvature regimes near the event horizon.
