  The present paper reviews our current understanding of the AGN component in
sub-mJy radio fields, as it results from the exploitation of multi-frequency
information available in two deep extra-galactic radio fields: the ATESP 5 GHz
sample and the First Look Survey. One of the key issues addressed here is
whether low-power AGNs are more related to efficiently accreting systems
(mostly radio-quiet) or to systems with very low accretion rates (mostly
radio-loud). The emerging picture is the following. Radio-loud jet-dominated
radio galaxies seem to be largely dominant down to flux densities of the order
of e.g. S>400 microJy. At lower flux densities (S(1.4 GHz) > 100 microJy)
radio-loud AGN are still present in significant numbers. However a population
of radio-emitting AGNs, whose properties are consistent with those expected
from existing radio-quiet AGN modeling, clearly shows up. This may indicate
that the bulk of the radio-quiet AGN population could emerge from studies of
deeper (S<100 microJy) radio samples. The radio-quiet AGN component could be
recognised thanks to the availability of IR colors which prove to be especially
useful to efficiently separate radio sources triggered by AGNs, from sources
triggered by star-formation.
