The paper deals in a general way with the whole field of instrument transformer work, and in a more extensive manner with certain developmets and views for which the authors are more particularly responsible. Among these are the following:—Current Transformers.— (i) Short-circuit limitations are described, the conclusion reached being that reduction of ampere-turns is the only real means of increasing the short-circuit capacity.(ii).Accurate transformers for metering.—The conclusions reached are that high accuracy can and should be obtained without recourse to a large number of ampereturns, and that single-turn or bar-primary transformers with compensating windings should be used on all heavy-duty circuits.(iii).The design and application of current transformers for Protective-gear systems.— The conclusions reached are that current transformers are not necessarily the limiting features in the performance of protective gear; but that transformers for protective systems can and should be designed to be “ideal transformers” as far as the requirements of the protective systems are concerned.Voltage Transformers.—(i) General features are described, the conclusions being that voltage transformers on low voltage circuits are a satisfactory proposition subject to suitable provision of protective fuses and resistors.(ii) On high-voltage circuits means of eliminating voltage transformers are described, by utilizing an existing power transformer, and connecting the voltage transformer to the low-votltage side and compensating for regulation of the power transformer.Special-purpose Instrument Transformers.— Design and application of current and voltage transformers with varying ratio characteristics are described, especially in regard to voltage or current-change amplifiers for the more sensitive operation of relays, voltage regulators, etc.