  The emergence of a new population of radio galaxies at mJy and sub-mJy levels
is responsible for the change in the slope of the radio source counts. This
population seems to include both star forming galaxies and classical
(AGN-powered) radio sources, but the relative importance of the two classes is
still debated. We present results from the ATESP radio survey and its optical
follow-up and show that the fraction of starburst galaxies changes from ~15% at
fluxes >1 mJy to >50% at lower fluxes.
