The surface and interface of nanomaterials play important roles in determining their catalytic properties. In this presentation, we will discuss, from the viewpoint of coordination chemistry, molecular mechanisms of several interfacial effects in the catalysis of metal nanomaterials [1]. The effects of surface ligands and supports on the catalytic performances of metal nanoparticles will be focused. Our strategies to create model nanocatalysts using well-defined nanocrystals and also atomically precise metal nanoclusters will be highlighted. Several examples will be given to illustrate how the interfacial species promote the catalytic activities and selectivities of metal nanomaterials: 1) Pt nanocrystals with sub-monolayer FeNi(OH)x grown on their surfaces were used to decode the interfacial effect of Pt-OH-M (M = Fe, Ni) in promoting catalytic CO oxidation [2]. 2) Atomically dispersed Pd catalysts were photochemically prepared to demonstrate the importance of chemical microenvironment in determining the catalysis of metal centers [3]. 3) Ultrathin Pt nanowires capped by ethylenediamine were synthesized to demonstrate the importance of electron-donating surface capping ligands in controlling the selectivity of catalytic hydrogenation [4]. 4) Ultrathin Ni nanosheets modified by trace surface sulfides were electrochemically prepared in situ to identify the HER active sites of transition metal chalcogenide nanocatalysts [5].