Piaget and his followers have articulated a complex theory of transition and change in intellectual behavior. Nearly a century ago, Freud proposed an elaborate theory of personality development in which some aspects of emotional growth were considered. We await the construction of a comprehensive theory of emotional development. Recognizing such a need, we set out over a decade ago to solve what seemed to be a relatively simple problem: By observing young children, could one successfully classify children in terms of individual differences on emotional dimensions such as happiness, fear, and anger? The task appeared easy. One could send graduate students into a preschool and ask them to observe children for several days, after which th ey would rank the children in terms of differences on various emo­ tional dimensions.