Symbiotic Union occupies a distinctive and theoretically charged position within the depth-psychological corpus, functioning simultaneously as a developmental stage, a transpersonal experience, a pathological configuration, and a neurobiological event. The term’s richest elaboration comes from two directions that rarely acknowledge each other: object-relations developmental theory, as mediated through Mahler’s separation-individuation schema and extended by Schore’s neurobiological synthesis, and Grof’s transpersonal phenomenology, wherein symbiotic unity with the mother is understood as the template for cosmic mystical experience. Fromm occupies a third position, treating the ‘symbiotic need’ as a socio-character formation that, when pathologically fixated, generates sado-masochistic relating rather than genuine love. Schore’s contribution is perhaps the most architecturally ambitious: he demonstrates, through converging neuroscience and developmental psychoanalysis, that visually mediated ‘merger’ experiences in the symbiotic dyad literally sculpt limbic circuitry, making early symbiosis constitutive of the neurobiological self. Grof, by contrast, traces the symbolic resonance of this primal union outward into transpersonal and cosmological registers, arguing that LSD subjects spontaneously recover intrauterine symbiotic experience as ‘oceanic ecstasy.’ The central tension in the corpus is whether symbiotic union represents a necessary and beneficent early state that must ultimately be relinquished, or whether its residues persist as both pathological liability and mystical resource throughout the lifespan.