The paper summarizes theoretical and practical investigations into the cause and properties of site errors at metre wavelengths. Attention is mainly directed to Adcock-type aerial systems; but other classes of instrument are considered in an Appendix. A criterion is there suggested to express the susceptibility of a direction-finder to site error, and is applied to well-known instrumental types.With some simplifying assumptions, the variations in error with azimuth and elevation angle due to “point”, “linear” and “sheet” type reflecting obstacles are examined. Certain properties of error charts which may be useful in locating the sources of error on a site are discussed. Errors introduced by randomly dispersed obstacles are considered from a statistical viewpoint.The theoretical and practical difficulties encountered in calibrating a site are discussed, the limitations of correction processes involving the use of previously measured error data being pointed out.Practical techniques available for locating the effective reflecting obstacles on a site are described, and examples of their application are given. Methods for suppressing unwanted reflections are considered.The work has led to a better understanding of site error phenomena at metre wavelengths, but further experimental work, linked with theoretical studies, is necessary.