Moral development refers to how children develop concepts of right and wrong based on social and cultural norms. Piaget and Freud proposed influential theories of moral development. Piaget viewed it as a constructivist process where interaction and thought build moral concepts. Freud believed moral development occurs when selfish desires are replaced by social values. Kohlberg's theory identified six stages of moral reasoning organized into pre-conventional, conventional, and post-conventional levels of increasing complexity. Social learning theory also views moral judgments as rule-governed behaviors acquired through observation and social interaction.