Randall Collins's interaction ritual (IR) theory suggests social solidarity as hardwired in the human neurological capacity for rhythmic entrainment. Yet, this article suggests that IR theory may benefit from being tied more firmly to recent neurobiological research, specifically Stephen W. Porges's polyvagal theory that proposes autonomic nervous system functioning as a basis for emotions and social behavior. In this perspective, IR theory does not sufficiently acknowledge the human nervous system as a system involving a phylogenetically ordered response hierarchy, of which only one subsystem supports prosocial behavior. The ritual ingredients of mutual attention and shared mood may, moreover, be specified as part of a social engagement system, neurally regulating attention and emotional arousal via a face–heart connection. The article suggests that this social engagement system provides part of the neural basis for rhythmic entrainment. The polyvagal theory furthermore challenges IR theory to reconsider the importance of individual biological differences—ritual success may not merely be ascribed to interactional effects, but also to reciprocal causality between situations and neurobiological properties of ritual participants.