Nanostructured materials possess unique optical and chemical properties that drive progress in optoelectronics, catalysis, and energy conversion. However, conventional nanoparticles lack atomic-level size control, limiting our understanding of structure–property relationships. Atomically precise nanoclusters, defined as discrete molecular entities, provide an ideal platform to unravel such correlations and enable rational design at the superatomic level. In this talk, I will present how synergistic atomic-level interactions in alloy nanoclusters, coupled with precise control over the local chemical environment and surface functionalization, markedly enhance catalytic performance in electrochemical CO₂ reduction and solar hydrogen generation. I will further discuss how core–shell engineering, heteroatom incorporation, and ligand modulation tune the electronic structure, offering molecular-level insights into reactivity and selectivity. Additionally, insights into interfacial water structure, charge distribution, and cluster–support interactions establish design principles for efficient, stable, and scalable catalysts. This integration of molecular understanding with application-driven design advances sustainable technologies for carbon-neutral energy and chemical production.