IN CONTRAST TO the abundant information about the health and development of children and about older adults, relatively little is known about young adulthood and midlife. Perhaps the bias in health and psychology toward the beginning and end of the life span is fostered by the abundance of striking changes that occur during those periods. However, from a life-span perspective there is continuity among all those phases. Genetic predispositions, as well as behaviors and attitudes learned as a child affect health in young adulthood, midlife, and old age. Although there are gaps in the information we have about health across the life span, more is being written about adulthood generally and about midlife in particular (Lachman & James, 1997). This chapter examines health and development during young, middle, and older adulthood.