Sexual behavior is activity that produces arousal and increases the chance of orgasm. Sex (sexual behavior and anatomy) is distinct from gender (being male or female).

Throughout most of human history, religion was the main source of information concerning sexuality. In the late 1800s and early 1900s, important contributions to the scientific understanding of sex were made by Sigmund Freud, Havelock Ellis, Richard von Krafft-Ebing, and Magnus Hirschfeld. These early researchers emerged from the Victorian era, in which sexual norms were highly rigid—although many people's actual behavior violated these norms. By the 1990s, major, well-conducted sex surveys were available. Today, the mass media are a powerful influence on most people's understanding of sexuality.

Studies of various human cultures around the world provide evidence of the enormous variations in human sexual behavior. For example, the frequency of intercourse may vary from once a week in some cultures to three or four times a night in others. All societies regulate sexual behavior in some way. Attitudes regarding premarital and extramarital sex, masturbation, same-gender sexual behavior, and gender roles vary considerably from one culture to the next. The great variations provide evidence of the importance of learning in shaping sexual behavior.

Within the United States, sexual behavior varies with one's social class and ethnic group. For example, African Americans are less likely to perform oral sex than whites are. In other areas, though, blacks and whites are quite similar. Traditional Latino cultures are characterized by rigid gender roles and restrictions on female—but not male—sexuality. Asian cultures tend to be conservative about sexuality for both males and females.

Studies of sexual behavior in various animal species show that masturbation, mouth-genital stimulation, and same-gender sexual behavior are by no means limited to humans. They also illustrate how sexual behavior may be used for a variety of nonsexual purposes, such as expressing dominance.