The Reionization of the intergalactic medium marks a turning point in the history of structure formation in the Universe. At present, the identification of the source population which ends up the Dark Ages and illuminates the Cosmic Dawn is still an open issue. Recent results from bright QSOs (M1450<-27) at z>4 observed by the Sloan survey indicate that they emit copious amount of ionizing photons, but their space density is still too low in order to reionize the Universe. Star-forming galaxies are more numerous but their escape fraction of ionizing photons is below few percent, still insufficient to keep the Universe ionized. Faint AGN could give an important contribution to the HI ionizing background and to the cosmic Reionization, depending on their abundance at low luminosities (L<0.1L*) and at high redshift (z>4). Recent results on the faint end of the AGN luminosity function at z>4 have been derived thanks to deep NIR observations with HST and faint X-ray detections in the 7Msec Chandra images in the CANDELS/GOODS-South field and in shallower CANDELS fields (GOODS-North and EGS). A dedicated spectroscopic survey with VLT and LBT starts to show that the ionizing escape fraction of faint AGN at z>4 is significant, and thus they can provide a fundamental contribution to the Reionization of the Universe.