The data-reduction and microscopic-model approaches to the determination of surface structure via analyses of elastic low-energy electron diffraction intensities are reviewed. Applications of both methodologies are discussed. Attention is focused on the evaluation of structural parameters for adsorbed layers of S and O on metals. In particular, the examples of Ni(100) − c(2 × 2) − S and Ni(100)−c(2×2)−O are examined in enough detail to reveal that the sulphur overlayer does not seem to lead to appreciable surface reconstruction whereas the oxygen overlayer can.