Attention is called to the advantages of the polyphase shunt commutator machine as an adjustable speed motor and also as an adjustable speed generator. The general theory of the shunt commutator motor is analitically and graphically explained. The simple methods of drawing the circle diagrams, which are sufficient for the practical calculations, is shown. Then, the influenoes of the design constants on the performance characteristics of the motor are considered. The practical design procedure of the polyphase shunt commutator motor is also explained. The comparison between the single winding and double winding motors is made. Finally, the experimental results relating to the twenty-five horse power three phase shunt commutator motor, designed by the author, are compared with the calculated results from the design data. The paper is divided into the following self-explanatory sections. Introduction. I-Three phase shunt commutator motor. II-The analytical calculations of the three phase shunt commutator motor. III-The circle diagram of the three phase shunt commutator motor. IV-On the design of the shunt commutator motor. V-The comparison of the double winding motor and the single winding motor. VI-Experimental results. VII-Summary and conclusion. Bibliography. List of symbols.