Abstract The characterization of surface structural defects by low energy electron diffraction is discussed. The identification of crystal mosaic structure, random strain, antiphase domains and steps is emphasized, and it is shown that they produce characteristic effects in the angular distribution of intensity in diffracted beams. Analytical models are summarized. They are also applicable to other surface-sensitive diffraction techniques such as reflection high energy electron diffraction and grazing angle X-ray diffraction. The quantitative analysis of these several types of defects is illustrated by measurements on the surface of an epitaxially grown Ag(111) film and on a sputter-etched and annealed GaAs(110) surface.