Developmental arrest occupies a contested but generative position in depth-psychological discourse, functioning simultaneously as a clinical descriptor, a metapsychological hypothesis, and an etiological cornerstone across multiple theoretical traditions. At its core the concept holds that psychological maturation may be halted, fixated, or structurally impeded at a specific phase, leaving the individual to organize experience—and ultimately personality—around the needs, defenses, and object-relational templates characteristic of that earlier moment. Freud’s libido theory provided the inaugural framework, wherein oral, anal, and phallic phases could each become sites of arrest or regressive return; subsequent theorists have substantially enlarged this terrain. Schore grounds developmental arrest in neurobiological process, arguing that failures of early dyadic affect regulation—specifically at rapprochement—produce measurable arrest of narcissism-regulatory structures. Flores and Khantzian carry the concept into addiction studies, treating substance dependence as, in part, a consequence of arrested self-care and affect-regulatory capacities rooted in faulty early attachment. Jung, characteristically, situates arrested mental development within familial and constitutional factors, while Beebe revisits the Freudian schema to argue that only introverted thinking could perceive how libido, once arrested, may leverage regression toward developmental advantage. Across these voices a tension persists: whether arrest is primarily structural and neurobiological, relational and intersubjective, or energic and symbolic—a tension that makes the term indispensable precisely because it bridges somatic, relational, and intrapsychic registers of explanation.