A review of research on AIDS preventive behavior indicates that minority and nonminority heterosexual adolescents and adults, gay men, injection drug users, and commercial sex workers are all less likely to practice safer sex with close relationship partners, compared with partners they perceive to be “casual” sexual partners. Because many individuals in close relationships have engaged in HIV risk behavior over extended periods of time and are unaware of their actual HIV status, practicing unprotected sexual intercourse with a committed relationship partner who is not tested for HIV appears to be a major and unrecognized source of HIV risk. This article reviews the evidence for higher levels of HIV risk behavior in close relationships and then presents relevant conceptual and empirical work to explore the psychological processes that may underlie risky sexual behavior in close relationships, using as a framework the information–motivation–behavioral skills model of preventive behavior.