In the last twenty years, X-ray surveys have revealed that a significant fraction of accretion through cosmic time is obscured. In this talk I will highlight some recent results obtained by combining the strength of deep X-ray observations (as those in the Chandra Deep Field North and South, and COSMOS) with optical/mid-IR information. In particular, mid-IR data, have been invaluable in offering complementary methods to select obscured AGN also in cases where the nuclear X-ray emission below 10 keV is largely obscured. The net effect of this multi-band observing strategy is to provide a more complete census of the obscured AGN population, hence clues to the AGN-galaxy co-evolution scenario, up to very high redshift (z~6). Prospects for forthcoming X-ray and mid-IR facilities will be also discussed.