Anxiety disorders have the highest prevalence of any group of mental disorders. This chapter primarily focuses on three of these anxiety disorders: generalized anxiety disorder, social anxiety disorder, and separation anxiety disorder. These three anxiety disorders have shared characteristics, are often comorbid, can continue into adulthood, and are predictors of other adulthood anxiety disorders. In schools, where many children and adolescents spend large quantities of time, anxiety can hinder academic performance, inhibit social relationships, and impact other important areas of functioning. Anxiety disorders in children or adolescents should be assessed using tools with empirical support and should include information triangulated from several sources. Treatment should cater to the level of need, such as cognitive-behavior therapy with individuals or groups. Collaborating with teachers, parents, and other community members is important for addressing anxiety thoroughly. A case example portrays these aspects of anxiety disorders in school-age youth.