Accretion onto supermassive black holes in Active Galactic Nuclei
(AGN) produces vast amounts of energy over optical, UV and X-ray
wavelengths from an accretion disc and corona; this primary emission
may then be reprocessed by a dusty torus surrounding the central
engine, giving rise to infrared emission and a number of AGN also
exhibit radio emission from jets.   Multi-wavelength studies are
therefore key in understanding how AGN work, and help us in
disentangling the diverse processes that are responsible for the
emission we see.   The energy output of an AGN can exert significant
influence on its immediate and distant surroundings, and in order to
obtain this energy budget due to accretion at a given epoch, it is
highly desirable to take simultaneous snapshots of AGN in optical, UV
and X-ray bands.  The infrared can also be used as a proxy for the
accretion emission, averaged over long timescales.  I will review past
and present work on AGN spectral energy distributions (SEDs) and the
determination of the total accretion energy budget, with a focus on
the hard X-ray selected Swift/BAT catalogue.  I will touch on
developments to come in an ambitious study of AGN SEDs proposed for
the latest version of this catalogue.