Human development theory, also known as developmental psychology, is a crucial field of study focused on understanding human growth and development across the lifespan. There are several synonyms for the term, including lifespan development, human growth theory, and developmental science. These concepts all refer to the study of the physical, cognitive, and social-emotional changes that occur as individuals progress through life. Other related terms include developmental psychology, child development, and adolescent development - each of which explores specific periods of the lifespan in greater depth. Regardless of what it is called, human development theory provides valuable insights into how people change and grow over time, and offers guidance for supporting optimal development in all individuals.