The concept of dissociative parts occupies a structural and clinical center of gravity within the depth-psychology literature on trauma, most fully elaborated in van der Hart, Nijenhuis, and Steele’s theory of structural dissociation of the personality. This framework, deeply indebted to Pierre Janet’s nineteenth-century psychology of action, posits that overwhelming trauma produces a rigid division of the personality into functionally distinct parts: Apparently Normal Parts (ANPs), oriented toward daily life action systems, and Emotional Parts (EPs), fixed in defensive action tendencies and saturated with traumatic memory. The corpus documents not merely the phenomenological variety of these parts—their degrees of emancipation, elaboration, amnesia, and mutual phobia—but insists on their systemic interdependence within a single organism. Courtois extends this framework clinically, emphasizing that therapeutic work must address the whole personality even when engaging individual parts, while Ogden approaches the same terrain somatically, attending to how dissociative parts carry procedural and implicit memory in the body. A sustained tension runs through the literature between the imperative to recognize parts as experientially real to the patient and the clinical necessity of neither reifying nor dismissing them. Integration—understood not as mere fusion but as synthesis, realization, personification, and presentification—is the governing therapeutic telos. The phobia of dissociative parts, and its treatment through graduated exposure and systemic intervention, constitutes one of the field’s most technically elaborated therapeutic challenges.