Given an imperfect crystal and an imperfect apparatus to measure the scattered intensity of low-energy electrons, the general problem is to determine the location of all atoms on, and in, diperiodic surface layers relative to a three-dimensional crystalline substrate. The immediate problem is to identify characteristic features in the experimental data (intensity profiles) that will indicate how the complete dynamic analysis may be reduced to yield a most probable structure in a given case; that is, how to identify the geometric signal in a background of multiple scattering “noise”? Recently proposed techniques for averaging out the primary effects of multiple scattering do, indeed, promise to provide the mechanism for unambiguous structure determination. With effective atomic scattering factors for low-energy electrons (also from averaging techniques) surface physics and chemistry can proceed on the same terms as solid state physics.