Abstract: Periodic two-dimensional arrays of identical metal clusters of nanometer size and spacing have been successfully fabricated on a Si(111) substrate by molecule beam epitaxy. The method used takes advantage of surface mediated clustering on a suitable template. The versatility of the method is demonstrated for a broad range of metals on Si(111)-7×7 substrates and the nano-dot arrays are stable up tp 200℃. In situ scanning tunneling microscopy analysis of In clusters, combined with first-principles total energy calculations, unveils unique initial-stage atomic structures of the surface-supported clusters and the mechanism of formation of these structures.