In the past decade, researchers have begun to study the sexual functioning of typical older persons. This review summarizes literature on the sexuality of men and women over age 50 as researched by social and health scientists. Research on the relationship of biological factors (changes accompanying aging), health (physical, mental, and medication use), psychological factors (attitudes, information about sex), relationship factors (status, satisfaction), and sexual functioning (desire, dysfunctions, treatment) to sexual behavior is reviewed. The review suggests that (a) men and women remain sexually active into their 70s and 80s, (b) aging-related physical changes do not necessarily lead to decline in sexual functioning, and (c) good physical and mental health, positive attitudes toward sex in later life, and access to a healthy partner are associated with continued sexual activity. In turn, regular sexual expression is associated with good physical and mental health. Progress in understanding later life sexuality requires development of comprehensive theoretical models, a broad focus on intimacy, attention to measures and samples, and research on couples. Progress in understanding is especially important, given the aging of populations.