Within the depth-psychology corpus, ‘Serenity’ occupies a peculiar double position: it functions simultaneously as a theological aspiration codified in recovery culture and as a psychological achievement pointing toward genuine ego-transcendence. The term’s most pervasive institutional form is the Serenity Prayer — attributed to Reinhold Niebuhr and canonized in Alcoholics Anonymous — which frames serenity not as passive repose but as the active acceptance of limitation, requiring courage and wisdom alongside surrender. Kurtz, Brown, McCabe, and the ACA literature all engage this formulation, reading it as an existential statement about the boundary between selfhood and the uncontrollable. A secondary current in the corpus, represented by Spiegelman and Dōgen, treats serenity as the phenomenological texture of contemplative attainment: the quality of sitting ‘alone, serenely,’ beyond striving, in which the ox and the rope of discipline have been forgotten. Feinstein’s psychophysiological research introduces serenity as a measurable state variable, placing it alongside interoceptive awareness in floatation-REST studies, thereby bridging contemplative description and neuroscientific operationalization. The tension between serenity as therapeutic tool (acceptance of powerlessness), spiritual fruit (post-struggle equanimity), and empirical parameter runs throughout the corpus and resists easy resolution. What unites these positions is the agreement that serenity is won, not given — that it emerges from the confrontation with limitation rather than from its avoidance.