Obscuration and Circumnuclear Medium in Nearby and Distant AGN

Some recent results on the physical and statistical properties of nearby and distant AGN are presented. I first discuss the properties of "elusive" AGNs, i.e. obscured AGNs which do not show a Seyfert-like spectrum in the optical. Then I present preliminary results from a detailed study of the contribution of obscured AGNs and of their host galaxies to the infrared cosmic background. Finally I discuss an observational program aimed at investigating the properties of the most distant quasars, of their circumnuclear medium and the implications for their host galaxies.