Transitional space — encompassing Winnicott’s foundational concepts of the transitional object and potential space — occupies a singular position in the depth-psychology corpus as the theoretical territory between inner psychic reality and the shared external world. Winnicott himself, across both Playing and Reality (1971) and The Maturational Processes and the Facilitating Environment (1965), insists that this intermediate area is neither purely subjective illusion nor objective fact, but a third domain where cultural experience, play, creativity, and religious feeling all take root. The corpus reveals several major lines of tension around this term. First, there is the developmental question: how the transitional object — the blanket corner, the soft jersey — functions as a bridge across the gap opened by maternal absence, gradually losing its discrete significance as its function diffuses across the whole cultural field. Second, writers such as Epstein (1995) extend Winnicott’s concept beyond infant development, arguing that meditative practice constitutes a transitional space of its own, one addressed not to the management of separation anxiety but to the dissolution of the acquired self’s defenses. Third, Kalsched (1996) reads the collapse of transitional space as a clinical signature of early trauma, in which the capacity for illusion and play is foreclosed and replaced by defensive encapsulation. Romanyshyn (2007) and Flores (1997) each relocate potential space within therapeutic and group contexts, demonstrating the term’s generativity beyond its origin in infant observation. The concept thus functions simultaneously as developmental milestone, clinical diagnostic criterion, and philosophical category.