Polymeric carbon nitride has been used with a certain success to produce hydrogen by photocatalysis exploiting its properties of wide-band gap semiconductor with band gap between 2.6 and 3.0 eV, which is suitable to split water into H-2 and O-2 (Delta E = 1.23 eV). Indeed, the conduction band (CB) edge is higher than the H-2/H+ potential as well as the H2O/O-2 potential is higher than the valence band (VB) edge. In addition, carbon nitride contains many active and coordination centers. This makes carbon nitride a very versatile material. However, the direct recombination of the pair electron and hole (exciton) removes energy to the redox reaction. This review is indeed focused on exciton recombination and localization, and on the efficiency of carbon nitride photosystems. Semiconductors and metals has been used to modify the properties of carbon nitride such as engineering the band gap, separating the exciton charges in order to increase hydrogen production. The hydrogen production of these systems coupling two photosystems, involving the Z-scheme, and co-catalysts is much higher than those based on pure polymeric carbon nitride or only on one co-catalyst. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.