In this work, the title of which rouses the utmost interest in every psycho-analyst, the two authors collaborate in treating the fundamental problems of psycho-analytic therapy from two points of view: the systematic and the critical-historical. An attempt of this sort occupies a peculiar position in psycho-analytical literature, for in one respect, namely, as a systematic synthesis, it is a novelty. Hitherto a fundamental enquiry into the underlying principles of psycho-analytic therapy and a systematic presentation of the mental processes during treatment have not been brought together within the scope of a single work. Freud himself, who from the beginning has guided with the intuitive certainty of the empirical scientist the development of the science which he created, for a very long time refrained from systematic works. He took the view that this experimental science, as yet in its infancy, should be accorded the greatest possible freedom in the formation of its concepts and that the directness of its observation should not be impeded by the premature construction of a