Abstract This chapter considers the study of developmental psychology, with a focus on the acquisition of age-appropriate social and emotional skills from infancy through adolescence and its role in child and adolescent mental health and social adjustment. In particular, our goals are to (a) provide a discussion of leading relevant developmental theories; (b) describe important dimensions of social and emotional development from infancy through adolescence at the behavioral and biological levels and within the context of interpersonal relationships; (c) provide a selective review of the associations between emotion regulation abilities, social adjustment, and indicators of early psychopathology; and (d) discuss challenges for future research in the field of developmental psychology, focused on social and emotional research that may inform our understanding of the development of mental health challenges for children and adolescents.