In the following account we have tried to review events more or less as they happened rather than to dissect component parts and give a separate review of the progress of each of them.Leopold Freund of Vienna, though not actually the first to use X rays therapeutically, may fairly be regarded as the father of radiotherapy. In November 1896, he irradiated a hairy mole with X rays and produced epilation. This was followed by the treatment of inflammatory conditions; and the use of X rays spread to various countries, and reports of patients treated soon appeared in Germany, Austria and America. Accounts of the response to X rays of superficial malignant conditions were published as early as 1900, and that of deep tumours in 1901.Dosage was determined by trial and error, and was complicated by the erratic behaviour of the apparatus. Accurate timing was impossible, as the platinum hammer-break of the coil kept on sticking, and the gas tubes of that day had no regulator. They began by being too soft, i.e., giving a longer wavelength, and then with working gradually became too hard. If, however, they were overheated they became so soft that they had to be put aside to recover. Their erratic behaviour persisted even when mica regulators were fitted; but they were definitely improved by the distantly-operated Bauer regulator which, by displacing mercury from a small disc of biscuit porcelain, allowed a little gas to enter the tube when required.