The book is focused on defense mechanisms as theoretical constructs as well as the possibilities of their empirical registration by different methods, and the application of these constructs in different fields of psychology with special regard to concurrent and predictive validity. It is argued that defense mechanisms are in many ways to be seen as integrative constructs, not necessarily restricted to psychoanalytic theory and that the potential fields of their application have a wide ranging scope, comprising many fields of psychology. Consequently empirical studies are presented from the fields of clinical and personality psychology, psychotherapy research and psychosomatic phenomena and diseases. Methodological questions have a heavy weight in most of these studies.