Reciprocity occupies a structurally pivotal position across several registers of the depth-psychology corpus. In the polyvagal literature — Porges, Dana — it designates the bidirectional, neurophysiologically grounded exchange between autonomic nervous systems that constitutes the precondition for safety, attachment, and co-regulation; its disruption triggers rupture and defensive withdrawal, its restoration repairs relational tissue. Ricoeur approaches reciprocity from a phenomenological-ethical direction, insisting that the norm of reciprocity — the Golden Rule in its multiple formulations — always presupposes an underlying asymmetry between agent and patient, and that genuine mutuality must be fought for against this structural inequality; friendship, solicitude, and the categorical imperative all converge on reciprocity as their regulative ideal. Seaford situates reciprocity in the archaic Greek economy of honour and gift-exchange, tracing how the monetisation of the polis both codified reciprocal harm and benefit under impersonal numerical equivalence and simultaneously destabilised the heroic order that depended on non-fungible personal reciprocity. Benveniste recovers reciprocity in the Indo-European gift-semantics, where the very morphology of words for ‘giving back’ discloses the structural compulsion of counter-gift. The I Ching tradition, via Wang Bi, names an entire hexagram Xian — Reciprocity — as cosmic mutual stimulation between complementary principles. Across these traditions, reciprocity is never merely exchange symmetry; it is the dynamic medium in which selfhood, ethics, and cosmological order are constituted and maintained.