Many adolescents are susceptible to negative outcomes associated with sexual behavior. This is particularly true for those who initiate sexual intercourse at an early age, have many sex partners, or engage in unprotected sex because these behaviors put one at risk for sexually transmitted infections (STIs), including HIV. This article reviews the various demographic, social-contextual, and intrapersonal factors linked to sexual risk behaviors. Successful STI/HIV prevention programs must consider developmental and gender issues, as well as cultural norms and values, to effectively meet the prevention needs of all adolescents. We discuss the characteristics of effective intervention programs and provide the names and key features of empirically validated, school-based STI/HIV prevention programs. In addition, we recommend specific roles for school psychologists in STI/HIV prevention efforts. Finally, other resources are provided to assist practitioners in their continuing review of STI/HIV prevention education. (Contains 1 table. A list of Relevant Websites and Publications is appended.)