There were four principal stages at which Freud made important innovations in the concept of repression or significant additions to it: the stage of introduction of the concept, 1894–6; the period 1900–6; the period 1911–15; the period 1923–9. The author makes a meticulous and exhaustive examination of Freud's writings in each of these periods, showing the contribution made to the theory of repression from his changing views on the nature of neurosis, and of normal psycho-sexual development; from the development of his metapsychological thought; and from his elucidation of psychic structure. Consideration is given to his final views on the question of primal repression, on the conditions which favour a return of the repressed, and to his views on the inter-relatedness of repression and other defence mechanisms.