Subnanometric metal clusters exhibit unexpected physical and chemical properties with potential applications in (photo)catalysis, energy conversion, sensing, bio-imaging, and theranostics. In the Perspective (http://doi.wiley.com/10.1002/sstr.202400147), María Pilar de Lara-Castells discusses fundamental concepts to understand their unique fluxional behavior in connection with conical intersections, resistance to deep oxidation, capability to make of titanium dioxide a visible photo-active material, highlighting challenges in their future through computational-theoretical modelling beyond the state-of-the-art.