Moral development focuses on the emergence, change, and understanding of morality from infancy through adulthood. In the field of moral development, morality is defined as principles for how individuals ought to treat one another, with respect to justice, others’ welfare, and rights. In order to investigate how individuals understand morality, it is essential to measure their beliefs, emotions, attitudes, and behaviors that contribute to moral understanding. The field of moral development studies the role of peers and parents in facilitating moral development, the role of conscience and values, socialization and cultural influences, empathy and altruism, and positive development. The interest in morality spans many disciplines (e.g., philosophy, economics, biology, and political science) and specializations within psychology (e.g., social, cognitive, and cultural). Moral developmental psychology research focuses on questions of origins and change in morality across the lifespan.