This article provides a comprehensive review of the prevalence and epidemiology of mental disorders in children and adolescents from community surveys worldwide. Despite methodological variations, the findings consistently indicate that approximately one-fourth of youth experience a mental disorder in the past year, and about one-third across their lifetimes. Anxiety disorders are the most common, followed by behavior disorders, mood disorders, and substance use disorders. However, only about half of youth with current mental disorders receive mental health specialty treatment, with those with severe disorders being more likely to receive services. Key issues in child psychiatric epidemiology include refining classification and assessment, including young children in surveys, integrating child and adult psychiatric epidemiology, and evaluating both mental and physical disorders in children. The article also highlights the need for national data to inform mental health policy and the increasing global efforts to address child mental health.This article provides a comprehensive review of the prevalence and epidemiology of mental disorders in children and adolescents from community surveys worldwide. Despite methodological variations, the findings consistently indicate that approximately one-fourth of youth experience a mental disorder in the past year, and about one-third across their lifetimes. Anxiety disorders are the most common, followed by behavior disorders, mood disorders, and substance use disorders. However, only about half of youth with current mental disorders receive mental health specialty treatment, with those with severe disorders being more likely to receive services. Key issues in child psychiatric epidemiology include refining classification and assessment, including young children in surveys, integrating child and adult psychiatric epidemiology, and evaluating both mental and physical disorders in children. The article also highlights the need for national data to inform mental health policy and the increasing global efforts to address child mental health.