Splitting occupies a foundational position in the depth-psychological corpus, operating simultaneously as a primitive defence mechanism, a developmental necessity, and a pathological fixation. Melanie Klein provides the most theoretically elaborated account: in the paranoid-schizoid position, the nascent ego actively splits both object and self into good and bad components, a process inseparable from projective identification and the management of persecutory anxiety. For Klein, splitting is not merely pathological but constitutive of early psychic life, becoming problematic only when it persists with excessive rigidity and prevents the integration characteristic of the depressive position. Laurence Heller, working within developmental trauma frameworks, extends this logic to somatic and relational registers: splitting is fueled by the child’s need to preserve attachment bonds by segregating aggression from love, and its resolution requires reclaiming disowned anger. Lisa Najavits applies the concept clinically to PTSD and substance abuse, where distinct ego-states alternate in a Jekyll-and-Hyde structure. Donald Kalsched, from an archetypal-Jungian vantage, frames splitting through dissociation driven by traumatic complexes. The I Ching tradition, represented across multiple translators, offers a cosmological counterpart in Hexagram 23 (Po/Splitting Apart), where structural disintegration precedes cyclical renewal. Across these registers, the critical tension is between splitting as adaptive defence and splitting as the obstruction of integration — the very dialectic that organises depth-psychological therapeutics.