The revolving-field theory as applied to single-phase induction motors is extended to develop a concise yet comprehensive theory for asymmetric three-phase induction motors. Each phase is represented by its equivalent circuit, not only to allow for uneven direct transformer interactions, due to asymmetric locations of phase windings, but also to account for the different number of turns, wire size, winding factor etc. each phase may have. The accuracy of the theory was confirmed by actual measurements on symmetric and asymmetric three-phase induction motors. Computed and test data on some motors are included for illustration. It is also shown that the general three-phase development can be easily applied to determine the behaviour of two- and single-phase induction machines, a useful feature for unified computer-aided design, by eliminating one and two phase windings, respectively. Not only the procedural details for determining the performance of single- and two-phase induction motors are given, but comparisons of numerical and test results on some output entities are included as well. Though the comparisons among theoretical and test results are made on fractional horsepower motors, the types being built at Universal Electric, the author is certain that the development presented here is equally applicable to all sizes of induction motors.