Optical and near-IR surveys, because of their large area, are exploring very efficiently supermassive black holes (SMBH) at high redshifts, z>5, and follow-up mm-observations, e.g. with ALMA, are offering an unprecedented view of the physical properties of their host galaxies. Optically selected AGN, however, may only form the tip of the iceberg as they are prone to obscuration. Many theoretical studies predict that the vast majority of these high redshift AGN are in fact heavily obscured. X-ray surveys represent the perfect tool to peer through obscuration and discover these hidden SMBH, but, owing to their limited area, have probed only a couple of tens AGN above redshifts of z=5. The situation is rapidly changing with the serendipitous XMM and Chandra catalogues and certainly with the eROSITA all-sky survey. In this meeting we will bring together the results coming from current optical and X-ray surveys, and from observations with state-of-the art mm and radio interferometers, trying to define solid paths for the future JWST, ATHENA, Lynx and AXIS surveys.