  In about four years, the National Aeronautics and Space Administration (NASA)
will launch a small explorer mission named the Imaging X-ray Polarimetry
Explorer (IXPE). IXPE is a satellite dedicated to the observation of X-ray
polarization from bright astronomical sources in the 2-8 keV energy range.
Using Gas Pixel Detectors (GPD), the mission will allow for the first time to
acquire X-ray polarimetric imaging and spectroscopy of about a hundred of
sources during its first two years of operation. Among them are the most
powerful sources of light in the Universe: active galactic nuclei (AGN). In
this proceedings, we summarize the scientific exploration we aim to achieve in
the field of AGN using IXPE, describing the main discoveries that this new
generation of X-ray polarimeters will be able to make. Among these discoveries,
we expect to detect indisputable signatures of strong gravity, quantifying the
amount and importance of scattering on distant cold material onto the iron
K_alpha line observed at 6.4 keV. IXPE will also be able to probe the
morphology of parsec-scale AGN regions, the magnetic field strength and
direction in quasar jets, and, among the most important results, deliver an
independent measurement of the spin of black holes.
