Social anxiety disorder is among the most common forms of pediatric psychopathology. Social anxiety symptoms peak in adolescence and are associated with significant impairment encompassing familial, social, and academic domains. Considerable heterogeneity in symptomatology, risk factors, and biological underpinnings exists across anxious adolescents, which has implications for (1) understanding the developmental etiology of who is at highest risk, (2) identifying individual patterns of symptom course. In particular, fearful temperament is the best early-emerging predictor of the development of anxiety symptoms, and attention bias to threat and other neurobiological processes have been implicated as mechanisms but it is unknown for whom and to what degree these factors impair functioning and what the developmental course looks like across adolescence. The current study employs a longitudinal design capturing a wide range of anxiety symptom presentation (i.e., low risk, temperamental risk, and clinical anxiety). We follow adolescents (N = 195) annually across the transitions to middle- and high-school – ages 13, 14, 15, & 16 years. We implement a rich assessment of anxiety symptoms, temperament, attention bias, endocrine (cortisol), physiological (RSA) and neurobiological (EEG, ERP) processes. We aim to (1) characterize a biobehavioral (i.e., biased attention, neuroendocrine, physiological, and neural processes) pattern associated with fearful temperament and social anxiety in adolescence, (2) characterize trajectories of social anxiety in adolescence, with an emphasis on linking fearful temperament and anxiety across development, and (3) examine how social contextual factors, sex, and pubertal development shape social anxiety trajectories and moderated links between temperament and SA.