This paper deals with fractional-slot multilayer windings. They are becoming attractive since they allow reducing the harmonic content of the magnetomotive force. Some examples of such a type of windings are reported in the literature, but they are limited to a few slot/pole combinations. On the contrary, in this paper, a general theory is presented. The main rules for the design of multilayer windings are illustrated. It is also investigated if the adoption of a multilayer winding makes possible the limitation of the torque ripple and the rotor losses of the machine. Several examples and experimental tests are reported to investigate the advantages and the convenience of adopting multilayer windings.