The interactive, give and take "dance" that highlights the synchrony between parents and young infants during social interaction occurs at the behavioral as well as the physiological level. These dyadic processes seen across infancy and early childhood appear to contribute to children's development of self-regulation and general socio-emotional outcomes. The focus of this chapter is on dyadic synchrony, the temporal coordination of social behaviors and the associated physiology. Research on behavioral, brain, and cardiac synchrony is reviewed within a bio-behavioral synchrony model. Tutorials for analyzing these types of complex social interaction data are noted.