Emotional fusion occupies a contested but structurally important position across the depth-psychology corpus, appearing at the intersection of Bowenian family-systems theory, Jungian archetypal psychology, and contemporary third-wave cognitive-behavioral frameworks. In the Bowenian lineage, as elaborated by Berger, emotional fusion names the failure of differentiation: the gravitational collapse of individual selfhood into an undifferentiated relational field, producing anxiety, reactive behavior, and what Berger terms ‘emotional prisons.’ The construct is fundamentally developmental — fusion is the unevolved condition from which a mature self must emerge. Neumann’s archetypal reading of the same phenomenon pushes further back, situating pre-egoic fusion in the participation mystique of primitive consciousness, where perception and instinctive reaction are coupled as a single reflex arc; the growth of ego-consciousness is precisely the story of disentangling from that primal state. In the ACT literature, Harris repurposes the cognate term ‘fusion’ in a strictly intrapersonal register — the conflation of self with thought-content — yet the structural logic mirrors Bowen: fusion arrests flexible response, and defusion (like differentiation) restores agency. Siegel’s interpersonal neuroscience offers a corrective: not all joining is pathological; ‘interpersonal integration’ distinguishes resonant linkage of differentiated individuals from the engulfing merger that obliterates boundaries. The central tension across these traditions is whether fusion is purely a deficit or whether some forms of primary union constitute necessary ground.