For more than 20 years the technique of short-circuit testing has been advanced steadily. To-day it has reached a high state of development, and it is opportune to examine the position. In the paper the characteristics of the main types of circuit-breaker are briefly summarized, and the various aspects of test-circuit severity are considered, both in relation to actual service conditions and to their effects upon the different types of circuit-breaker. Existing test procedures and methods are reviewed, and suggestions are made for the improvement of some of them and for their being brought more into line with present service requirements. Proposals are also made for methods of approach to certain tests which it has not yet been possible to standardize. Particular attention is paid throughout to the problems associated with the testing of large circuit-breakers. Finally a brief reference is made to the part played by field tests and the requirements of a modem testing station.