Abstract: Social neuroscience has recently shifted from a focus on one-brain activation to research on two-brain communication during social interactions. In this talk, I will present our theoretical model on biobehavioral synchrony and discuss how it offers a new perspective on human sociality and its affiliative origins. The talk will present three studies on brain-to-brain synchrony using hyperscanning EEG from three developmental stages. The first study examined how adult attachment relationships (romantic love, close friendship) shape inter-brain synchrony as mediated by behavioral coordination and the task at hand. The second study tested the effects of maternal chemosignals on infant-adult brain-to-brain synchrony, and the third compares inter-brain synchrony during "live" versus technologically-assisted communication between adolescents and their mothers. Finally, I will describe the use of inter-brain synchrony methods to specify mechanisms of change in the treatment of depressed mothers and their infants. The talk will end by addressing the implications of the model to the neurobiology of resilience and its utility for fine-tuning the construction of targeted interventions.