  Most of the action in Active Galactic Nuclei (AGN) occurs within a few tens
of gravitational radii from the supermassive black hole, where matter in the
accretion disk may lose up to almost half of its energy with a copious
production of X-rays, emitted via Comptonization of the disk photons by hot
electrons in a corona and partly reflected by the accretion disk. Thanks to its
large effective area and excellent energy resolution, Athena+ contributions in
the understanding of the physics of accretion in AGN will be fundamental - and
unique - in many respects. It will allow us to map the disk-corona system -
which is crucial to understand the mechanism of energy extraction and the
relation of the corona with winds and jets - by studying the time lags between
reflected and primary photons. These lags have been recently discovered by
XMM-Newton, but only Athena+ will have the sensitivity required to fully
exploit this technique. Athena+ will also be able e.g. to determine robustly
the spin of the black hole in nearby sources (and to extend these measurements
beyond the local Universe), to establish the nature of the soft X-ray
components, and to map the circumnuclear matter within the AGN inner parsec
with unprecedented details.
