Photocatalytic water splittingPhotocatalytic water splitting, the process of using light energy to split water molecules into hydrogen and oxygen, has garnered significant attention for its potential in clean energy production. This process offers a promising solution to the global energy crisis by utilizing solar energy to produce hydrogen fuel, a clean alternative to fossil fuels. However, the efficiency of photocatalytic water splittingPhotocatalytic water splitting heavily depends on the use of suitable photocatalystsPhotocatalysts, which are materials that absorb light and facilitate the necessary reactions. CocatalystsCocatalysts play a crucial role in enhancing the performance of photocatalystsPhotocatalysts, by accelerating reaction kinetics, improving selectivity, and stabilizing the overall process. This chapter provides a comprehensive overview of the role of cocatalystsCocatalysts in photocatalytic water splittingPhotocatalytic water splitting. We discuss the mechanisms through which cocatalystsCocatalysts function, their effects on reaction rates, and their contribution to optimizing the efficiency of photocatalytic systems. Furthermore, we examine the key materials used as cocatalystsCocatalysts, their interactions with photocatalystsPhotocatalysts, and recent advancements in this rapidly evolving field.