Since the appearance of the author’s _Selected Papers on Hysteria and other Psychoneuroses_, and _Three Contributions to the Sexual Theory_,[A] much has been said and written about Freud’s works. Some of our readers have made an honest endeavour to test and utilise the author’s theories, but they have been handicapped by their inability to read fluently very difficult German, for only two of Freud’s works have hitherto been accessible to English readers. For them this work will be of invaluable assistance. To be sure, numerous articles on the Freudian psychology have of late made their appearance in our literature;[B] but these scattered papers, read by those unacquainted with the original work, often serve to confuse rather than enlighten. For Freud cannot be mastered from the reading of a few pamphlets, or even one or two of his original works. Let me repeat what I have so often said: No one is really qualified to use or to judge Freud’s psychoanalytic method who has not thoroughly mastered his theory of the neuroses—_The Interpretation of Dreams_, _Three Contributions to the Sexual Theory_, _The Psychopathology of Everyday Life_, and _Wit and its Relation to the Unconscious_, and who has not had considerable experience in analysing the dreams and psychopathological actions of himself and others. That there is required also a thorough training in normal and abnormal psychology goes without saying. _The Interpretation of Dreams_ is the author’s greatest and most important work; it is here that he develops his psychoanalytic technique, a thorough knowledge of which is absolutely indispensable for every worker in this field. The difficult task of making a translation of this work has, therefore, been undertaken primarily for the purpose of assisting those who are actively engaged in treating patients by Freud’s psychoanalytic method. Considered apart from its practical aim, the book presents much that is of interest to the psychologist and the general reader. For, notwithstanding the fact that dreams have of late years been the subject of investigation at the hands of many competent observers, only few have contributed anything tangible towards their solution; it was Freud who divested the dream of its mystery, and solved its riddles. He not only showed us that the dream is full of meaning, but amply demonstrated that it is intimately connected with normal and abnormal mental life. It is in the treatment of the abnormal mental states that we must recognise the most important value of dream interpretation. The dream does not only reveal to us the cryptic mechanisms of hallucinations, delusions, phobias, obsessions, and other psychopathological conditions, but it is also the most potent instrument in the removal of these.[C] I take this opportunity of expressing my indebtedness to Professor F. C. Prescott for reading the manuscript and for helping me overcome the almost insurmountable difficulties in the translation.