The Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood-Revised (DC: 0-3R) is a developmentally based diagnostic manual that provides clinical criteria for categorizing mental health and developmental disorders in infants and toddlers. It is organized into a five-part axis system. The book has been translated into several languages and its model is widely adopted for the assessment of children of up to five years in age. The Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood-Revised (DC: 0-3R) is a developmentally based diagnostic manual that provides clinical criteria for categorizing mental health and developmental disorders in infants and toddlers. It is organized into a five-part axis system. The book has been translated into several languages and its model is widely adopted for the assessment of children of up to five years in age. The DC 0-3R is meant to complement, but not replace, the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), and the International Statistical Classification of Diseases and Related Health Problems (ICD-10) of the World Health Organization. It is intended to enhance the understanding of young children by making it possible to assess, diagnose, and treat mental health problems in infants and toddlers by allowing for the identification of disorders not addressed in other classification systems. The DC: 0-3R is organized around three primary principles: 1) that children’s psychological functioning unfolds in the context of relationships, 2) that individual differences in temperament and constitutional strengths and vulnerabilities play a major role in how children experience and process events, and 3) that the family’s cultural context is important for the understanding of the child’s developmental course.