The waning moon occupies a significant and consistently shadowed position within the depth-psychology corpus. Across Jungian, archetypal, and astrological-psychological traditions, it functions as the emblematic image of decremental process: the movement from fullness toward darkness, from fertility toward sterility, from visibility toward concealment. Jung himself, in his 1928–1930 seminars, anchors the waning moon firmly in millennia of folk experience, documenting its universal association with decay, ghostly danger, and agricultural failure — a primordial impression encoded in the collective unconscious. Thomas Moore, drawing on Ficino’s Neoplatonism, rehabilitates the waning phase as a therapeutically indispensable moment: without the emptying that waning enacts, no genuine fullness is possible, and resistance to this natural decay represents a pathological loss of Luna. Von Franz reads the moon’s waxing and waning alchemically, as the corruptible, restless character of the feminine that the coniunctio seeks to stabilize. Liz Greene situates the waning within the full lunar cycle as a phase of decreasing light that ancient observers experienced as treachery. The central tension in the literature runs between the waning moon as omen of ruin (Jung’s folk register, Greene’s archaic dread) and as necessary psychological rhythm (Moore’s therapeutic reframing). Together, these positions insist that the waning moon is not pathology but an archetypal station in the soul’s own cyclical economy.