This document summarizes several theories of adult development, including age/stage, life events, and transitions theories. Age/stage theorists like Levinson, Gilligan, Havighurst, Maslow, Gould, and Erikson see development as proceeding through distinct stages linked to age. Life events theorists such as Neugarten, Baltes, and Riegel link development to major life occurrences. Transitions theorists like Bridges and Sugarman view development as a series of transitions between life phases.