The definition of strategies for preventing STD and AIDS requires a better knowledge of sexual behavior in the general population and in specific subgroups of the population. Surveys have been undertaken in different countries to provide such information, and they allow to draw some general conclusions. Even if there exist a very important variability of sexual behaviors between individuals and within individuals in different situations, the primary characteristics of sexual behavior in different developed countries appear to be quite similar. All prevention efforts need to be directed toward everybody in the population, but they must in the same time be made age specific, gender specific, and culture specific. The repertoire of available methods must be expanded to offer different choices, taking into account important psychological and sociologic determinants of sexual behavior. The development of methods under women's control would permit to combine the goals of contraception and of STD prevention.