Ego possession designates a condition in which an autonomous psychic content — a complex, an archetypal figure, or an affect-laden unconscious force — usurps the executive function of the ego, displacing its characteristic will, discrimination, and reality-testing with the agenda of the possessing factor. The depth-psychology corpus approaches this phenomenon from several converging angles. Jung and his immediate heirs treat possession as the phenomenological signature of complex autonomy: when a complex erupts into consciousness it does not merely colour ego experience but temporarily replaces it, so that the individual acts, feels, and perceives from within the complex rather than in relation to it. Edinger elaborates the specific modalities — anima possession in men, animus possession in women — showing how the absence of a ‘solid, functioning ego’ to relate to an archetypal figure allows that figure’s negative qualities to prevail. Neumann locates the mechanism in the structural relationship between ego-consciousness and the unconscious, arguing that the ‘triumphant grin of the unconscious’ at having taken possession of the ego is the hallmark of neurotic and psychotic dysfunction. Woodman’s clinical glossary crystallises the definitional core: where a strong ego relates objectively to activated complexes, its failure appears as possession. The overarching clinical and ethical stakes concern whether consciousness can maintain sufficient differentiation to sustain genuine relationship with unconscious contents, or whether it collapses into identity with them — a collapse that Neumann terms the ego’s ‘identification with the persona’ and Edinger terms inflation.