The paper explains the need for high-voltage impulse generators which will produce the standard voltage waveshapes specified for impulse testing. A theoretical analysis of the impulse generator and load circuit is given, and the development of the multi-stage generator for high voltages is described. The mechanism of operation of the multi-stage generator is analysed and is illustrated by oscillograms. Illustrations of two typical generators are shown, and some of the auxiliary equipment needed is briefly mentioned. The paper concludes with an example of impulse-testing technique.