Rhythmic synchrony occupies a distinctive and underexplored position within the depth-psychology corpus, appearing at the intersection of somatic healing, interpersonal co-regulation, coordination dynamics, and cosmological thinking. The term names the phenomenon by which two or more oscillatory systems — bodies, brains, persons, or even person and cosmos — entrain to a shared temporal pulse, with consequences held to be psychologically and physiologically significant. McNiff reads its disruption as the very mechanism of psychosis, framing mental disturbance as an acute loss of synchrony with nature’s rhythmic ground. Schore situates interpersonal rhythmic synchrony at the core of attachment, arguing that the caregiver’s modulation of the infant’s biological rhythmic patterns is the foundational act of emotional development. Siegel and colleagues draw on coordination-dynamics research to show that interpersonal synchrony emerges as a self-organizing property when two oscillating systems couple sufficiently to overcome their differing natural frequencies. Haeyen demonstrates the clinical deployment of rhythmic synchrony in polyvagal-informed creative-arts therapy, where percussion and vocal matching stimulate the ventral vagal system and install co-regulation. McGilchrist situates rhythmic entrainment within his broader argument for the primacy of dynamic, becoming-oriented experience over static analytic categories. Campbell reaches toward the cosmological register, reading the alignment of heartbeat with astronomical cycles as the mythopoetic kernel of ancient rhythmic cosmologies. The central tension across these voices is whether synchrony is primarily a therapeutic instrument, a neurobiological mechanism, or an ontological fact about the structure of living systems.