2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14840We discuss the constraints on the AGN evolution from the cosmic X-ray background and source counts. A synthesis model to fit the X-ray background is presented. In the model, the spectrum of type 2 AGN has been modeled including Compton down--scattering within the absorbing material. Besides, we introduced a dependence on redshift of the relative number of obscured sources and found a decrease of the fraction of type 2 AGN at redshifts larger than 2.8 pages, 7 figures, accepted for pubblication in A&AAstrophysicstext