This Research Topic was launched with the aim of highlighting and exploring the mechanisms and functions of interpersonal interaction, and thereby deepening our understanding of these highly interesting and complex phenomena and their downstream effects on real-life social interaction. The collection of contributions includes a Hypothesis and Theory article, a Review, two Brief Research Reports, and 11 Original Research articles written by leading researchers in the field. They showcase the breadth of research studies, going from hyper-brain cell assembly hypothesis and theory of mind hyperscanning to ensemble singing and soccer playing to healthcare teams, music therapy and psychotherapy concepts based on the inter-brain plasticity model. This range exemplifies the promise of this field in being able to span multiple facets of life. Figure 1 illustrates the diversity yet thematic relatedness of the contributions. It displays the joint forward model for interpersonal action coordination with three representation levels (i.e., representation of individual, other's, and joint forward models with corresponding sensorimotor feedbacks) and the impact of a joint goal as well as external influences (cf. Müller et al., 2021). This model is a construct integrating and reflecting a variety of influences and interactions of human social behavior. Figure 1 also highlights different interaction situations described in the Research Topic.