This article reviews the clinical features, epidemiology, leading theories, and treatment of anxiety and related disorders. Although anxiety-based disorders share a number of core features, there are fundamental differences between these conditions in terms of feared stimuli, emotional responses (e.g., anxiety, panic, and fear), maladaptive beliefs and cognitive biases, and problematic behaviors that serve to maintain symptoms. Despite these differences, a number of treatment approaches, such as exposure techniques, cognitive restructuring, and relaxation exercises, have resulted in positive effects across a range of anxiety-based disorders. This article ends with a discussion of these approaches.