Epidemiologic surveys consistently document that anxiety disorders are the most prevalent class of mental disorders. This chapter reviews the prevalence and distribution of DSM-IV anxiety disorders across the life span, drawing predominantly on large-scale epidemiologic surveys conducted in developed regions of the world, where the most rigorous work has been conducted. Sex differences in the prevalence of anxiety disorders are consistent across cultures and survey methods. Across cultures, epidemiologic work typically finds women to be at greater risk for social anxiety disorder (SAD) than men. Across several DSM iterations, generalized anxiety disorder (GAD) has evolved from a non-specific residual anxiety category to its current status as a primary anxiety disorder. Across cultures, lifetime panic disorder (PD) rates range roughly from 2% to 4%, and 1-3% reports the presence of PD within the past year. Increased efforts are needed to document population- based prevalence estimates of childhood anxiety disorders.