This work was originally issued as a two-volume set, published in 1987 and 1988. It constitutes the definitive presentation of the system of classifying moral judgment built up by Lawrence Kohlberg and his associates over a period of twenty years. Researchers in human development and education around the world, many of whom have worked with interim versions of the system - indeed, all those seriously interested in understanding the development of moral judgment - will find it a useful and accessible resource. Volume 1 reviews Kohlberg's stage theory, and the large body of research on the significance and utility of his moral stages. Issues of reliability and validity are addressed. The volume ends with detailed instructions for using the reference sections, which are presented in volume 2.