The Société Nationale des Chemins de Fer Français (S.N.C.F.) has ordered 105 electric locomotives (85 C0–C0and 20 B0–B0) for the electrification of the Valenciennes–Thionville line.The general principles which governed their selection are put forward, and the reasons which led to the adoption of single-cab locomotives are explained. The manner in which the problems of visibility of signals and current collection were solved is fully described. An analysis of the annual costs of different types of electric locomotive under French conditions is also included.Two types of C0–C0locomotive, one with a single-phase d.c. generator set and one with a single-phase/3-phase rotary convenor, are described, and the considerations which affected the choice of output and the determination of the maximum running speed are given. A comparison is drawn between the efficiency of these locomotives and that of other types. The methods adopted to improve adhesion and to secure the hauling of trains heavier than those drawn by 1,500-volt d.c. French locomotives are examined in detail.A survey of the B0–B0locomotives is then given. The qualities of the motor adopted for the locomotives with single-phase motors is stressed, while the manner in which the locomotives equipped with ignitrons differ from those previously constructed is described.