Quasars and Seyfert 1 (Sy1) galaxies, their lower-luminosity siblings,
(AGN is used to refer to quasars and Sy1 galaxies hereafter)
are multi-wavelength emitters, with roughly equal energy output
extending from the far-infrared (FIR) through to the X-ray region in all
AGN, with extensions to radio and/or high energy
-rays
in ~ 10%. Technological advances, particularly in the infrared (IR), mm,
X-ray and
-ray regions, have led to a
dramatic increase in multi-wavelength
observations of AGN over the past decade or so. This, in turn, has led
to fundamental improvements in our understanding of the energy
generation mechanisms at work in these powerful objects. This paper
reviews the current status of our observational knowledge and
the energy generation mechanisms responsible for what we see.