This document discusses theories of identity development during adolescence. It begins with early theories from G. Stanley Hall that viewed adolescence as a turbulent period from ages 12-25 driven by physiological changes. Erikson's psychosocial theory from the 1940s proposed that identity versus identity confusion is the main task of adolescence. James Marcia later operationalized Erikson's theory into four identity statuses based on exploration and commitment: diffusion, foreclosure, moratorium, and achievement. The document then discusses theories of ethnic identity development from Phinney and extensions from Phinney and Devich-Navarro regarding identification with one's ethnic group and the majority culture.