Abstract The development of the large steam turbine, which has taken place within recent years, is largely attributable to the rapid growth of the electric-power industry, and the records of performance of fourteen turbines varying in capacity from 30,000 to 70,000 kw. which the author presents and which cover a period of four years, are accordingly of interest in showing the reliability of such large units and exceedingly valuable as evidence of the service to be expected. The design of such large units naturally presents many problems, and those relating to steam areas, rotor speed, blade proportion, number of stages and rotor dimensions are dealt with by the author at some length. The construction of such large units also involves many problems, and those dealing with exhaust chambers, cylinders, bearings, oil-circulating and cooling systems, couplings, etc., are briefly discussed.