It is shown that the performance of an induction motor, having a symmetrically wound rotor and a stator which may be wound or connected in any conceivable way, can be uniquely specified by means of two sets of equations. The first set, the `internalÂ¿ equations, is peculiar to the machine and expresses the phase voltages in terms of the phase currents and rotating-field parameters. These are based on a generalization of the counter-rotating field theory to include the effects of all space harmonics. The second setÂ¿the `externalÂ¿ equationsÂ¿is peculiar to the connection and expresses the relationships between the phase voltages and currents, supply voltages and line impedances. These are the so-called `inspection equationsÂ¿ obtained by the simple application of Kirchhoff's laws. The complete performance of the machine can always be computed from the solutions of the two sets of equations on a phase-by-phase basis. It is also shown that, if the stator has windings whose axes are symmertically displaced, symmetrical-component theory is an alternative which enables to be computed on a per-phase basis whilst still including the effects of all space harmonics.