The structures of adsorbed metals on single crystal surfaces of other metals have been reviewed and tabulated. Most of the adsorbates of over 100 systems studied form ordered surface structures that may undergo changes as the coverage in the monolayer is increased. At low coverages the adsorbate and substrate surface structures are closely related indicating the predominance of the adsorbate–substrate interaction in determining ordering. At higher coverages there are more complex ordering characteristics. Although the relative atom sizes and magnitudes of adsorbate–substrate and substrate–substrate interactions influence the ordering in the monolayer general conclusions that have predictive value must await the avialability of more experimental results on more metal adsorbate–substrate systems.