AbstractElectrocatalytic water splitting is regarded as one of the most promising strategies for producing clean and sustainable energy sources (H2 and O2) in cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), respectively. Currently, transition metal nanoparticles (NPs) such as commercial Pt/C, IrO2, and RuO2 are still popular catalysts for industrial‐level HER and OER processes. However, both the high cost and low atomic utilization of NPs can not satisfy the requirements of atomic economy and green chemistry. Compared with NPs, metallic nanoclusters (NCs), which have higher atom utilization and optimized electronic structure than NPs, show unique activities for water splitting. In this review, the recently reported advanced design strategies for preparing various NCs are discussed in detail. The methods to control the particle size, coordinated environment, and morphology of NCs are also summarized. The electrochemical activity and stability of NCs can be influenced by the synergistic effect between NCs and supporting materials, which is also mentioned. Then, the recently reported state‐of‐art‐catalysts for both HER and OER along with the detailed catalytic mechanism are described to show the advanced design principles. Finally, the future perspectives and some remaining challenges are also presented.