  The main properties of AGN are reviewed, focussing on the accretion process
and on the question of whether AGN are the best factories of ultra high energy
particles and photons. I recall the large differences between the
accretion/ejection flows in strong and weak accretors, and I conclude that,
since low luminosity AGN and even "dormant" massive black holes in nuclei of
galaxies are powering strong confined magnetized jets able to accelerate high
energy particles, and are present in a large proportion of galaxies, they might
be better potential sources of high energy particles and photons than luminous
AGN and powerful radio galaxies.
