Many methods for investigating surfaces are sensitive to a layer several atoms deep. It is difficult to distinguish the separate contributions from successive layers. One approach to the study of a single atomic surface layer of a metal is to look at epitaxial adsorbed metal overlayers. Some results from this approach and the prospects for ’’two-dimensional metallurgy’’ are surveyed. The following topics are included: the existence of adsorbed metallic monolayers from thermodynamic and kinetic considerations; surface diffusion; the structure and composition of adsorbed metallic monolayers examined by LEED and AES; melting and solid–solid phase changes; surface alloying and binary monolayers; surface defects and implications for clean surface behavior.