Photocatalysis has been recognized to be a promising process for the energy and environmental applications. Eventually, photocatalytic materials are largely modified in their physical and chemical structures. The former involves the size and shape dependent properties, while the latter involves the process of doping, composites, co-catalyst loading, etc. The doping process conventionally includes the cationic substitution, where it largely modifies the conduction band of the photocatalyst, not the valence band. However, the modification of VB is also required for the fine tuning of band edge potentials of the photocatalyst towards developing them for their versatile photocatalytic applications. In this direction, oxynitrides-based semiconductors demonstrate the possibilities of simultaneous tuning of the potential energy of VB and CB to construct the photocatalytic materials for the favorable and sustainable photocatalytic process. Accordingly, this review has been constructed to provide insights into the materials and mechanism of metal oxynitrides for their various photocatalytic applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.