The paper deals with the application of electromagnetic theory to electrical machines. A digest of the existing information, hitherto published piecemeal, is presented in a unified form by classifying diverse methods of analysis. Also a method, not available in the literature surveyed, is given to account for the presence of space harmonics. It is indicated how the field equations can be applied to single-phase machines. Inductance formulas are derived from the field equations, and their experimental verification is included. Unpublished work is given in detail, and published material is summarised. An attempt is made to include a complete bibliography on the subject.