This volume is to examine the phenomena of non-disclosure in its wide ranging forms, study its properties, and to deepen the capacity of a mental health professional --as well as all clinicians who provide mental health counseling -- to detect and engage it across a range of clinical settings. Unengaged, sustained DNDD represents an impasse that is destructive to a clinician’s capacity to both understand and treat a patient. Successfully engaged, on the other hand, DNDD offers a unique perspective on in individuals anxieties, presuppositions, and mental functioning. A clinician who is both aware that a patient is withholding information, and comfortable with that awareness, may approach the patient material while listening for both indications of non-disclosed material and—critically—a growing awareness of psychopathology or other motivational forces driving non-disclosure.