This document discusses defense mechanisms according to Sigmund Freud and later theorists. It begins by defining defense mechanisms as unconscious mental processes that the ego uses to reduce anxiety. It then outlines Freud's concepts of the ego, id, and superego and how they relate to anxiety. The document proceeds to summarize different theorists' contributions, including Anna Freud's focus on defenses operating against anxiety and George Vaillant's classification system. It provides examples and descriptions of different defense mechanisms, grouping them into narcissistic-psychotic, immature, neurotic, and mature categories. Overall, the document provides a comprehensive overview of psychoanalytic theories and classifications of defense mechanisms.