During the past 25 years, a great deal of research and theory has addressed the development of young children´s understanding of mental states such as knowledge, beliefs, desires, intentions, and emotions. Although developments in children´s understanding of the mind subsequent to early childhood has received less attention, in recent years a growing body of research has emerged examining understanding of psychological functioning during middle and late childhood. Combined with the literature on adolescent epistemological development, this research provides a broader picture of age-related changes in children´s understanding of the mind. Guided by the goals of describing developmental changes in children´s concepts of cognitive functioning and identifying sources of information that contribute to learning about cognition, 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.