Developmental psychology is the scientific study of how and why human beings change over the course of their lives. This field is concerned with various aspects of development, including physical, cognitive, emotional, and social development. Here are some major theories and theorists in developmental psychology:

1. Psychosexual Development Theory
   • Theorist: Sigmund Freud
   • Description: Focuses on how early childhood experiences, particularly concerning sexual drives and pleasure centers, shape personality development. Freud’s theory includes five stages: oral, anal, phallic, latency, and genital.
2. Psychosocial Development Theory
   • Theorist: Erik Erikson
   • Description: Builds upon Freud’s theories, but Erikson focused on social experiences across the entire lifespan. His theory consists of eight stages, each of which is characterized by a particular psychosocial conflict, such as trust vs. mistrust, or identity vs. role confusion.
3. Cognitive Development Theory
   • Theorist: Jean Piaget
   • Description: Piaget’s theory focuses on how children acquire knowledge and how their cognition changes over time. He identified four stages of cognitive development: sensorimotor, preoperational, concrete operational, and formal operational.
4. Socio-Cultural Theory
   • Theorist: Lev Vygotsky
   • Description: Emphasizes the role of social interactions and culture in the development of cognition. Vygotsky’s theory is particularly focused on how language acquisition aids a child in learning about the world.
5. Ecological Systems Theory
   • Theorist: Urie Bronfenbrenner
   • Description: Proposes that a person’s development is influenced by their environment and the systems they interact with, ranging from their immediate family to society as a whole. The theory is divided into several levels, including the microsystem, mesosystem, exosystem, and macrosystem.
6. Social Learning Theory
   • Theorist: Albert Bandura
   • Description: Focuses on the importance of observational learning, imitation, and modeling in behavior development. It posits that individuals learn and adopt new behaviors by observing others and modeling their actions.
7. Attachment Theory
   • Theorist: John Bowlby, Mary Ainsworth
   • Description: Deals with the importance of attachment in regards to personal development. It primarily focuses on the attachment between infants and their primary caregivers and how this affects social and emotional development.
8. Identity Development Theory
   • Theorist: James Marcia
   • Description: An extension of Erikson’s Psychosocial Development Theory, focusing on the development of identity in adolescence. Marcia’s theory revolves around four identity statuses – identity achievement, moratorium, foreclosure, and identity diffusion.
9. Theory of Mind
   • Theorist: Various contributors (Premack & Woodruff initially coined the term)
   • Description: Focuses on understanding that other people have beliefs, desires, intentions, and perspectives that are different from one’s own. It is a crucial aspect of social cognition that develops primarily during early childhood.
10. Multiple Intelligences Theory
    • Theorist: Howard Gardner
    • Description: Proposes that humans possess different kinds of intelligences rather than being dominated by a single general intelligence. These include linguistic, logical-mathematical, spatial, bodily-kinesthetic, musical, interpersonal, intrapersonal, and naturalist intelligences.
11. Object Relations Theory
    • Theorists: Melanie Klein, Donald Winnicott, Harry Guntrip, and others
    • Description: A branch of psychodynamic psychology that focuses on the way individuals form enduring mental representations and attachments to others based on early childhood experiences.
12. Moral Development Theory
    • Theorists: Lawrence Kohlberg, Carol Gilligan
    • Description: Focuses on the evolution of moral reasoning as individuals age. Kohlberg’s model involves three levels of moral development, each containing two stages. Carol Gilligan, a critic of Kohlberg’s model, proposed a different approach to moral development based on the ethic of care.

These theories encompass various aspects of human development, from cognitive and moral development to attachment and identity formation. They provide frameworks for understanding how individuals grow and change throughout their lives.