The paper compares the d.c. and 16⅔-c/s single-phase systems of electric traction, examines the problem of the choice of a particular system and shows why 50-c/s single-phase distribution was adopted. The advantages conferred and the economies made possible by this system are discussed, and the various types of locomotive drive which it allows are detailed. Some indication of the merits of each is given.Special attention is paid to the C0–C0locomotives using single-phase/d.c. and single-phase/3-phase motor-generator sets, which are of particular advantage for hauling the numerous heavy freight trains on the Valenciennes–Thionville line and may be adapted for working at unity power factor.B0–B0locomotives will be used to haul the majority of other traffic over many electrified main lines. The main drives employed are the single-phase motor and the d.c. motor with ignitron conversion, for which a great future is predicted.