Piaget's theory of cognitive development states that our cognitive abilities develop through four specific stages.
Attachment theory, developed by John Bowlby and Mary Ainsworth, describes the dynamics of long-term relationships between humans.
Freud's psychosexual theory of development suggests that children develop through a series of stages related to erogenous zones.
Erikson's psychosocial stages of development focus on the resolution of different crises to become a successful, complete person.
Kolhberg's theory of moral development states that we progress through three levels of moral thinking that build on our cognitive development.