Mortificatio occupies a singular position in depth-psychological literature as the most extreme and consequential of the alchemical operations: the deliberate killing, blackening, and decomposition of psychic material as a necessary precondition for renewal. Edward Edinger provides the most sustained treatment, establishing mortificatio as the operation that comprehends darkness, defeat, torture, mutilation, death, and putrefaction — all unified under the hallmark color black, the nigredo. Edinger insists that these images are not merely metaphorical imports from metallurgical procedure but genuine projections of psychological experience onto the laboratory vessel, making mortificatio a drama of the psyche enacted in matter. James Hillman, approaching the same terrain through imaginal psychology, reads mortificatio as the askesis of torturing that produces complete blackening — a total killing of the life of the material, exhaustive and unsparing. Both writers inherit Jung’s foundational understanding of alchemy as a projection of the individuation process, wherein the suffering of matter encodes the suffering of the soul. Andrew Samuels situates mortificatio within an ordered sequence — nigredo, fermentatio, mortificatio, putrefactio — marking it as the stage at which original elements cease to exist in their initial form. Plato’s equation of philosophy with a preparation for death, the Gnostic injunction to become seekers for death, and the Christian imagery of crucifixion and Passion all converge in the analytical literature as paradigmatic mortificatio narratives. The term thus functions as a crucial hinge between destruction and transformation in the depth-psychological reading of the alchemical opus.