The Principium Individuationis occupies a structurally foundational position in the depth-psychological corpus, functioning simultaneously as an ontological principle, a cosmological drama, and a clinical imperative. Jung’s earliest and most compressed formulation appears in the Septem Sermones ad Mortuos, where the term names the creature’s essential drive toward distinctiveness against the undifferentiated nothingness of the Pleroma — dissolution into which constitutes literal psychic death. This Gnostic framing, preserved verbatim in Memories, Dreams, Reflections and echoed by Edinger, establishes the term’s double valence: individuation is simultaneously the creature’s highest calling and its most perilous adventure, since the intensification of individual selfhood concentrates — and therefore mirrors — the infinite Pleromatic fullness. Jung’s alchemical writings extend this into the mercurial spirit motif, where the principium individuationis becomes a force that can be wrongly imprisoned by spiritual authority, linking the concept to Schopenhauer’s and Buddhism’s ambivalence about selfhood as the root of suffering. Nietzsche’s Birth of Tragedy deploys the term in its Schopenhauerian register as the Apollonian principle of bounded form against Dionysian dissolution. Simondon’s philosophical project, while never citing Jung, constitutes a parallel and competing account, displacing the principle from substance (form or matter) onto process itself — onto ontogenesis, metastability, and transindividuality. Together these voices pose the central tension: is individuation a principle defending selfhood against chaos, or is it itself the problem that a deeper philosophy of relation must overcome?