This chapter presents nosological models for early childhood psychopathology embodied in the Diagnostic and Statistical Manual of Mental Disorders (DSM), fifth edition, and the International Classification of Diseases, 10th revision. It also presents the revised Diagnostic Classification of Mental Health and Development Disorders of Infancy and Early Childhood as another nosological approach that provides more differentiated diagnostic categories and criteria for early childhood disorders. As an alternative to the top-down nosological approaches based on experts’ concepts of disorders, the chapter presents bottom-up approaches that statistically derive dimensional syndromes from ratings of problems in large samples of children. Statistically derived syndromes have been supported by data from multiple informants in dozens of societies around the world. The data from these societies have been used to construct multicultural norms for the syndromes, for DSM-oriented scales, and for broad-spectrum Internalizing, Externalizing, and Total Problems scales. Case illustrations are provided for translational applications in medical, mental health, educational, and child or family service settings.