Mental disorders are just as common in young children as they are in older children, but they are often not adequately recognized and treated. This textbook aims to provide a comprehensive, well-founded, and practice-relevant overview of the variety of mental disorders from birth to school entry. The textbook is based on interdisciplinary guidelines, new classification systems, current research findings, and the author's many years of practical experience. Each disorder is presented in detail, with specific recommendations for diagnosis and therapy.