Lawrence Kohlberg developed a theory of six stages of moral development based on Jean Piaget's and John Dewey's work. Kohlberg's stages are grouped into three levels - pre-conventional, conventional, and post-conventional. At the pre-conventional level, morality is based on obedience and self-interest. The conventional level is characterized by conforming to social norms. The post-conventional level involves reasoning based on universal ethical principles rather than rules. Progression through the stages is sequential and depends on cognitive disequilibrium when one's thinking is challenged by moral dilemmas.