If the fullest advantage is to be gained from the rapid developments which have taken place in connection with radiant and high-frequency methods of heating, care must be exercised in the selection of the applications for which they are recommended. Although many processes can be carried out more effectively by the new methods, there is still a very real place for contact and convective heating. The purpose of the paper is to facilitate this selection.The paper first reviews the various methods of heating, indicating the physical laws and practical considerations by which they are governed and the rates of heating which may be obtained. An endeavour is then made to classify, in terms of their technical requirements, the types of application for which each process is best suited. Finally, several specific applications are considered in some detail, and it is shown that processes having a superficial similarity may never-theless possess features which are of sufficient importance to warrant the use of different methods of heating.