Intact social functioning relies on a combination of explicit and implicit behavioral, attentional, and interpersonal processes referred to as "social cognition". Characterizing these interpersonal processes forms a critical underpinning to understanding and treating psychopathology, particularly in disorders where deficits in social functioning do not emerge as a secondary symptom but rather as an essential feature of the disorder. Two of such disorders are autism spectrum disorders (ASD) and schizophrenia spectrum disorders (SZ). However, despite the substantial overlap in the features of social dysfunction between ASD and SZ, including social cognitive deficits in theory of mind, perspective-taking, and empathy, there is a limited understanding of the mechanisms underlying those shared deficits, and how to treat them. We suggest that disruptions of interpersonal functioning emerge over the course of development, and that interpersonal synchronization, a phenomenon in which behavioral and physiological cues align between interacting partners, forms a critical component of social cognition that underlies the disruption in social functioning in ASD and SZ. We present a conceptual review of typical and atypical development of social processes and highlight the role of interpersonal synchronization across the course of development. Then, we review the existing evidence suggesting impairments in both the intentional and spontaneous synchronization of interpersonal processes in ASD and SZ, as well as studies suggesting that interpersonal synchronization and clinical symptoms may be improved through body-oriented interventions within these disorders. Finally, we suggest potential mechanisms that may underpin typical and atypical development of interpersonal synchronization.