Defensive exclusion stands as one of John Bowlby’s most theoretically consequential contributions to depth psychology, functioning as his information-processing reformulation of classical repression. Drawing on cognitive psychology and neurophysiology rather than drive theory, Bowlby articulates defensive exclusion as the active inhibition of significant information from further conscious processing — a mechanism he locates at the heart of psychopathology, placing it in direct structural parallel with Freudian repression while freeing it from metapsychological assumptions he found scientifically untenable. The corpus reveals Bowlby developing this concept across the Attachment and Loss trilogy, with its fullest elaboration in the 1980 volume on Loss, where he distinguishes the ordinary, adaptive exclusion of information (necessary to prevent cognitive overload) from its pathological, defensive variant, which operates to forestall the pain and terror associated with acknowledged loss. Crucially, Bowlby argues that vulnerability to initiating defensive exclusion is maximal in the earliest years of life, that parental pressure — including threats of abandonment — is a primary causal condition, and that the resulting deactivation of behavioural systems underlies chronic mourning, dissociative states, and depressive disorder. The concept bridges attachment theory, cognitive science, and clinical practice, establishing how what cannot be known or felt — because a caregiver forbids it — becomes structurally excluded rather than simply forgotten.