Model oxide-supported metal cluster catalysts have been prepared by evaporating the corresponding metal (e.g., Cu, Pd, Ni) onto a oxide thin film (~100 Å), which in turn is supported on a refractory metal (Mo, W, Ta) surface. The deposited metal films, upon annealing, form small metallic clusters on the oxide surface whose size are dependent upon the initial metal film thickness. The surface structures and cluster morphologies have been characterized using scanning probe microscopies, temperature-programed desorption, X-ray, and ultraviolet photoemission; and high-resolution electron energy loss spectroscopy/infrared reflection-absorption spectroscopy of adsorbed carbon monoxide. The catalytic properties of these clusters have also been investigated with respect to several reactions including CO/O 2 and CO/NO. The chemical and electronic properties of the metal clusters with respect to size are compared to the analogous properties of extended single crystal surfaces.