This paper present theoretical calculations of reflectance anisotropy spectra (RAS) for overlayers of alkali atoms adsorbed on a crystalline metallic surface. We assume that the overlayer is formed by an ordered twodimensional (2D) array of adatoms that respond to the local electric field like point‐like harmonic oscillators. We consider overlayers with several rational coverages, assuming that the adsorbates occupy high symmetry sites which form a Bravais lattice that is commensurate with the substrate [1,2]. RAS spectra are obtained for the five 2D Bravais lattices. We found that RAS can be used to observe ordered phases when the ordered phase has a rectangular, centered‐rectangular or oblique symmetry. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)