Three theories of defense and adaptation by Brenner, Modell, and Kohut are critically appreciated and compared with special reference to the variety of ways in which these concepts have been extended beyond the realm of internal ho-meostasis. Each theory is discussed in terms of its value or limitations in elucidating the theoretical ego or experiential self and object. The three theories are also compared regarding how and to what extent each theory suggests and forecloses lines of interpretation in the clinical context.