Adulthood is usually defined as the period of human development in which the physical development, cognitive development, and psychosocial development of women and men slow and reach their highest level. Although scholars strive to build consistent theories, the description of the developmentally highest level differs between countries and cultures due to economic factors and sociocultural factors. After presenting some basic concepts of adulthood from different cultures, this entry continues with a psychological definition of adulthood, a discussion of characteristics of maturity, and brief descriptions of various theories about what constitutes adulthood. It ends with suggestions for the direction of future discussions on adulthood.