Heavily obscured AGN with BeppoSAX, INTEGRAL, SWIFT, XMM and Chandra: prospects for Simbol-X

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.