  According to the latest versions of synthesis modeling of the Cosmic X-ray
Background, Compton Thick AGN should represent ~50% of the total absorbed AGN
population. However, despite their importance in the cosmological context, only
a few dozens of Compton Thick AGN have been found and studied so far. We will
briefly review this topic and discuss the improvement in this field offered by
the Simbol-X mission with its leap in sensitivity (E>10 keV) of more than a
factor 500 with respect to previous X-ray missions.
