  Violent activity in the nuclei of galaxies has long been considered a
curiosity in its own right; manifestations of this phenomenon include distant
quasars in the early Universe and comparatively nearby Seyfert galaxies, both
thought to be powered by the release of gravitational potential energy as
material from the host galaxy accretes onto a central supermassive black hole
(SMBH). Traditionally, the broader study of the formation, structure and
evolution of galaxies has largely excluded active galactic nuclei. Recently
however, this situation has changed dramatically, both observationally and
theoretically, with the realisation that the growth and influence of the SMBH,
the origin and development of galaxies and nuclear activity at different epochs
in the Universe may be intimately related. I review the intriguing evidence for
causal links between supermassive black holes, nuclear activity and the
formation and evolution of galaxies, and describe opportunities for testing
these relationships using the next generation of earth-bound and space-borne
astronomical facilities. (Abridged)
