A sex difference in libido does exist. Men report desiring sex more frequently, with more partners, and with more variety compared with women. Sex differences in masturbation are large and consistent. Women and girls are less likely to masturbate than men and boys, and some evidence indicates that male individuals who masturbate do it more frequently than female individuals. Most studies on extramarital sexual activity have found that men report more partners than women. In both heterosexual and homosexual relationships, men have more frequent and more varied fantasies than women, and men report thinking about sex more often than women. Living without sexual gratification is easier for women than for men. Although sexual desire declines with age for both sexes, most men retained at least occasional sexual desire, whereas the great majority of women articulated no sexual desire. In the authors’ view, the mentioned issues may explain the imposition of Hijab on women and the allowance of polygamy for men.