Child development can be described across physical, cognitive, and social/emotional domains from conception through adolescence. Numerous theories have attempted to explain child development, including psychoanalytic, behaviorist, biological, cognitive, and systems theories. The document provides an overview of the major 20th century theories of child development, including those proposed by Freud, Erikson, Watson, Skinner, Bandura, Piaget, Vygotsky, Bowlby, Bronfenbrenner and others.