Despite the central importance of sexuality to human well-being, the study of sexuality remains marginalized within health psychology, which hampers the ability of clinicians and policy-makers to promote comprehensive health and well-being. In this review we discuss the evidence that sexual functioning makes critical contributions to human health, focusing specifically on findings linking sexual activity to morbidity and mortality, to the health-promoting effects of intimate relationships, and to processes of emotion regulation. We argue that researchers studying the psychology of health and well-being should more substantively integrate sexuality into their research agendas. Health psychologists’ specific expertise in investigating and interpreting complex, reciprocal associations between subjective emotional states, health-relevant cognitions, and health-relevant behavior can make a notable contribution to elucidating some of the most intruiging correlations between sexuality and health that have emerged from medical and epidemiological studies. If we want to foster optimum physical and mental health among youths and adults, we must rigorously investigate the multiple mechanisms through which positive sexual functioning plays a unique and fundamental role in human well-being across the life course.