  In this paper we give a brief review of the astrophysics of active galactic
nuclei (AGN). After a general introduction motivating the study of AGNs, we
discuss our present understanding of the inner workings of the central engines,
most likely accreting black holes with masses between a million and ten billion
solar masses. We highlight recent results concerning the jets (collimated
outflows) of AGNs derived from X-ray observations (Chandra) of kpc-scale jets
and gamma-ray observations of AGNs (Fermi, Cherenkov telescopes) with jets
closely aligned with the lines of sight (blazars), and discuss the
interpretation of these observations. Subsequently, we summarize our knowledge
about the cosmic history of AGN formation and evolution. We conclude with a
description of upcoming observational opportunities.
