Published information on the impulse breakdown of high-voltage cables of the solid and gas-pressure types is summarized with particular reference to the effect of the testing variables on the impulse strength.An impulse generator and its associated measuring equipment for performing tests on cables are briefly described.Details of measurements of the impulse strength of solid-type and gas-cushion cables are given, and reference is made to impulse-strength experiments on impregnating compound and impregnated paper, and on cable models.The impulse breakdown process in high-voltage cables of these types is discussed in relation to the properties of their constituent dielectric materials.