Piaget systematically attempted to relate cognitive, moral, and emotional development in infancy, childhood, and adolescence. In his view, cognitive and emotional development show parallel, complementary courses of development, with cognition providing the structure and emotion the energy of development. Just as children go through stages of cognitive development, they likewise display emotional development that can be thought of as containing qualitatively new emotional expressions and experiences which are characteristic of different levels of development. Although emotional development is closely tied to cognitive development in infancy, it appears to be more closely related to moral and social development in childhood and adolescence. This paper (1) briefly summarizes Piaget's explicitly held position on the relationship between emotional, cognitive, and moral development; (2) presents a reconstruction of Piaget's data on infants', children's, and adolescents' emotions; and (3) compares Piaget's explicit theoretical statements about emotional, cognitive, and moral development with the reconstruction of his database. It is concluded that Piaget's "data" support his theoretical claims, and that the close connection between cognitive and emotional development during infancy paves the way for the equally close link between emotional and moral development during childhood and adolescence. (RH)