Identification of the active catalytic site and design of catalysts with 100% atomic efficiency has been a long-standing goal in heterogeneous catalysis. From the point of view of catalytic materials that can be used to optimize fuel processing and hydrogen production, and the production of value-added chemicals from various feedstocks, there is an urgent need for high-performance and stable catalysts that comprise only trace amounts of precious metals. Atomically dispersed supported metal catalysts offer new prospects for low-cost fuel processing and green chemicals production (Annu. Rev. Chem. Biomol. Eng. 2012, 3). In this presentation, metal catalysts prepared as single atoms on various supports will be reviewed drawing examples from a variety of reactions, including the low-temperature water-gas shift reactions, methanol steam reforming, and methanol and ethanol dehydrogenation and selective oxidation reactions. We will demonstrate how reaction mechanisms hold over the continuum of structures from the single atom to nanoparticles, if the former is identified as the active site. Novel synthesis methods will be discussed as will be the stability of atomically dispersed catalysts in various reaction environments. Ample scope for novel catalyst design for more sustainable processes has emerged from these studies.