To understand how AGN accrete, evolve and affect the surrounding galaxy, it is necessary to investigate how their intrinsic properties change with time. We consider different AGN populations, accounting for the physical properties and obscuration, and trace their redshift evolution. In particular, we investigate the role of Eddington ratio and accretion efficiency in the black hole mass function, and build a scenario where objects with a high spread in Eddington ratios, including low values (10^-3-10^-2) are consistent with the observed local mass function.