Complex possession names the condition in which an autonomous complex displaces or overwhelms the ego, temporarily seizing its functions and installing itself as a surrogate center of personality. The depth-psychology corpus treats this phenomenon with unusual seriousness precisely because it straddles the boundary between ordinary psychopathology and archaic experience. Jung himself supplied the foundational coordinates: complexes, as ‘splinter psyches,’ assimilate the ego when unconsciousness is sufficiently pronounced, producing the ‘momentary and unconscious alteration of personality’ that earlier centuries designated possession by spirits or demons. The Middle Ages, Jung noted with pointed irony, had the more accurate metaphysics. Murray Stein extends this into a nosological continuum, distinguishing the mild dissociative state of being ‘in complex’ from the full fragmentation of multiple personality disorder, with complex possession occupying an intermediate register. Marion Woodman, working from clinical material on eating disorders and addictions, treats possession by complex as the operative mechanism linking body symptom to psychic configuration, enumerating it systematically alongside projection and inflation. Kalsched situates the phenomenon within trauma theory, showing how the self-care system’s inner objects — both protective and persecutory — are complexes whose autonomous energy constitutes a form of possession. Across these positions, a key tension persists: whether possession by complex is pathological rupture to be remediated or, as Samuels and the archetypal tradition suggest, the necessary dramatic form through which psychic energy achieves recognition and eventual integration.