Adolescents who experience social anxiety concerns often display symptoms and impairments when interacting with unfamiliar peers. For adolescent clients, reducing symptoms and impairments within these interactions comprises a key treatment target within exposure-based therapies for social anxiety. Recent work on mechanisms of change in exposure-based therapies highlights the need for therapeutic exposures to simulate real-world manifestations of anxiety-provoking social situations. Yet, researchers encounter difficulty with gathering ecologically valid data about social interactions with unfamiliar peers. The lack of these data inhibits building an evidence base for understanding, assessing, and treating adolescent clients whose concerns manifest within these social interactions. Consequently, we developed a paradigm for understanding adolescent social anxiety within social interactions with unfamiliar peers. In this paradigm, we train peer confederates to interact with adolescents as if they were a same-age peer, within a battery of social interaction tasks that mimic key characteristics of therapeutic exposures. Leveraging experimental psychopathology and multi-modal assessment approaches, this paradigm allows for understanding core components of social interactions with unfamiliar peers relevant to exposure-based therapy, including stimuli variability, habituation, expectancy violations, peers' impressions about socially anxious adolescents, and maladaptive coping strategies that inhibit learning from exposures (e.g., safety behaviors). We detail the conceptual and empirical foundations of this paradigm, highlight important directions for future research, and report "proof of concept" data supporting these research directions. The Unfamiliar Peer Paradigm opens new doors for building a basic science that informs evidence-based services for social anxiety, within clinically relevant contexts in adolescents' social worlds.