What is known about adolescent sexual behavior is reviewed. First, the onset of sexual behavior in the teenage years is considered as a function of cohort, gender, and ethnic differences. Omissions in the research on sexual behavior other than intercourse are highlighted. Possible biological, social, and social cognitive processes underlying teenage sexual behavior are then considered. Next, demographic trends in the use of contraceptives and antecedents of regular birth control use are reviewed. Finally, some of the successful program initiatives directed toward altering sexual and contraceptive practices are discussed, keeping in mind the importance and relative lack of well-designed and carefully evaluated programs.