Physiological synchrony, or concordance, among caregiver-child dyads involves the matching of biological states. Understanding this process is critical for enhancing our knowledge of the ways that the caregiver-child relationship supports child development. However, the meaning of physiological synchrony for child adjustment is poorly understood. This study examined physiological synchrony in respiratory sinus arrhythmia (RSA), an indicator of parasympathetic activity, between 87 mothers (M age = 35.30 years, SD = 6.71 years) and their preadolescent children (M age = 10.36 years, SD = 1. 19 years, 52.9% girls). Dyads, all of which were from economically impoverished backgrounds, participated in 3 tasks that varied in the level of interaction that was required between the partners. Mothers self-reported their own depressive symptoms and rated their children's externalizing and internalizing symptoms. Physiological synchrony was generally strongest in tasks requiring the greatest levels of interaction among partners. Further, RSA synchrony was positive in the context of low levels of maternal depressive and child internalizing symptoms, and negative in the context of high levels of such symptoms, though results varied by task. Child externalizing symptoms did not moderate the RSA concordance process. The results identify both proximal and distal contexts in which physiological synchrony occurs, which ultimately broadens our understanding of the meaning and significance of parent-child physiological synchrony.