Sacred Reciprocity, as the depth-psychology corpus treats it, names the mutual, bidirectional exchange through which psychic life — whether between nervous systems, between ego and Self, or between the human and the divine — is constituted and sustained. The concept carries at least three distinct registers across the literature. In the neurobiological register, Dana and Porges ground reciprocity in polyvagal theory: the autonomic nervous system is a relational organ whose ventral vagal circuits require the ebb and flow of giving and receiving, attunement and resonance, to maintain the neuroception of safety that underlies attachment and meaning. Rupture and repair are understood as the dialectical rhythm through which reciprocal connection is deepened rather than dissolved. In the depth-psychological and alchemical register, Jung, Edinger, and von Franz locate sacred reciprocity in the coniunctio and hierosgamos — the covenantal blood-bond between Yahweh and Israel, the Mercurial fountain that perpetually replenishes itself, and the opus magnum as a transformative exchange between ego and the unconscious. In the comparative-religious register, Campbell, Welwood, and the I Ching tradition frame intimate relationship itself as a sacred path whose very friction is the crucible of soul. The unifying tension across all registers is whether reciprocity names a biological given or a spiritual achievement — or whether that distinction finally holds.