The paper is based on a survey of main-line locomotives of new design put into service during the last decade, and Tables giving the more important details of these units are appended.An attempt is made to find general tendencies in design, but it is realized that the somewhat limited data available relating to each particular class of locomotive or design feature may admit more than one interpretation, and the Tables have therefore been made as comprehensive as possible sothat those interested may be able to form their own conclusions.In the Introduction attention is drawn to the growing demand for locomotives of greater power and speed, partly to meet improved running schedules with heavier trains and partly to avoid the higher cost of multiple operation.The paper is divided into two sections dealing with mechanical components and electric equipment respectively, and each feature of interest is considered separately.The outstanding change in mechanical design is the widespread adoption of individual-axle drive in preference to rod drive, and the types most extensively used are dealt with in some detail. Changes in electric equipment have consisted largely of detailed improvements, and little basically new apparatus has appeared except on two lines where the introduction of locomotives with entirely novel equipment has made possible the use of a single-phase supply of industrial frequency.