This article uses concepts from cognitive psychology to illuminate an important distinction proposed by Wallerstein (1967, 1983) between defense mechanisms versus defense contents and behaviors, which differ in important ways with consequences for such theoretical issues as the pathogenicity of defense, the role of defense in supportive psychotherapy, and the sense in which defenses are unconscious. Although defense contents and behaviors can be unconscious in Freud's dynamic sense, an understanding of the unconscious status of defense mechanisms requires an extension of the concept of the unconscious to include what Sandler and Joffe (1969) called the “nonexperiential” (p. 81). Although Brenner argued against Wallerstein's distinction, this article shows how their differences can be resolved.