Children’s discovery of the active mind organizes empirical literature concerning the development of children’s knowledge of cognitive activities from early childhood to adolescence and presents a conceptual framework that integrates children’s introspective activities with social influences on development. Bringing together theoretical and empirical work from developmental, cognitive, and social psychology, the author argues that rather than depending upon a single source of information, developmental progress is driven by combinations of children’s conceptual knowledge of mental functioning, children’s phenomenological awareness of their own cognitive activities, and children’s social experience.