This review focuses on developmental aspects in the epidemiology of anxiety disorders including prevalence, onset, natural course, longitudinal outcome, and correlates and risk factors, with focus on childhood through young adulthood. Anxiety disorders are frequent and early-emerging conditions. They may remit spontaneously; however, the same or other mental disorders often recur. Although risk factors have been identified, more work is needed to identify the most powerful predictors for onset and the progression to more complex forms of psychopathology and to understand the underlying mechanisms and interactions. This identification is crucial to facilitate research prevention, early interventions, and treatment programs.