The literature on High Frequency Currents is not extensive and most of it is too technical for the average physician, who is more interested in the application of these currents than he is in the pre cise manner in which they are generated. For this reason I have given comparatively little space to the consideration of the various forms of apparatus, other than to outline the types upon one or another of which all of the machines are based. Further information along this line is properly within the sphere of the various manufacturers. My intention has been to make this a practical hand-book for the busy physician Who Wishes to use high frequency currents and to learn how to do so with as little red tape as possible. I have expressed my individual Opinion on many points, and sometimes this may be found at variance with that of other authors, but it is based upon nineteen years' practical experience involving the daily use of High Frequency Currents and upon six teen years' experience in teaching the subject.