Decay occupies a charged and multivalent position across the depth-psychological corpus, refusing reduction to mere biological dissolution. The tradition consistently treats decay as a psychologically active condition — one that carries regenerative, diagnostic, and even teleological significance. The I Ching’s hexagram Ku (18), rendered in both Wilhelm traditions as ‘Work on What Has Been Spoiled [Decay],’ anchors the philosophical pole: decay is the consequence of stagnation arising from human freedom misused, and therefore demands active remediation — it is not fate but failure, and not final. Hillman reads decay through the Saturn-senex complex: the archetype harbors an ‘appetite for decay and negation’ as intrinsic to the same psychic structure that creates order, making decay a depth-psychological necessity rather than pathology. Thomas Moore, drawing on Ficino’s planetary psychology, explicitly rehabilitates lunar decay — the waning moon — as essential to psychic rhythm, warning that resistance to ‘natural decay and waning’ constitutes a pathological loss of soul. Neumann locates Egyptian dread of bodily decay at the heart of mortuary culture, distinguishing it sharply from the Germanic embrace of death. The alchemical tradition, as read by Hillman, understands decay as one transitional quality within a temporal process of transformation. Across these positions, the recurring tension is between the ego’s drive toward immortality and permanence and the soul’s requirement for dissolution, emptying, and return.