Identification, introjection, incorporation, and internalization dealt with the same basic process according to S. Freud. The process has been discussed and researched in many and varied personal-social contexts. There have been two general areas of concern: identification for positive reasons (often called developmental) and identification for negative reasons (often called defensive). The latter is the true Freudian mechanism, triggered in the unconscious ego because of unpleasure, threat or anxiety. Of course, Freud used the concept identification in different ways, as have others during and since his times. Our bibliography emphasizes identification, introjection, incorporation, and internalization as defense mechanisms, and includes studies between the late 1920's and the middle 1920's. (Author)