Sexual orientation is defined as a person's erotic and emotional attraction toward members of his or her own gender, toward members of the other gender, or both.

The majority of Americans believe that homosexuality is wrong. This belief is the basis for much antigay prejudice. In some cases this prejudice is so strong that it results in hate crimes and harassment directed at gays and lesbians.

Lesbian, gay, and bisexual communities can be found around the world. These communities are defined by a common culture and social life and by rituals such as pride marches.

In surveys, the majority of gay men and lesbians report being in a steady romantic relationship. Although concerns have been voiced about the sexual orientation and psychological well-being of children who grow up in lesbian and gay families, these concerns are unfounded, according to the available studies.

The most recent well-sampled surveys indicate (when corrected for some underreporting) that about 2 percent of men and 1 percent of women are exclusively homosexual and that roughly 10 percent of men and 10 percent of women have had at least one same-gender sexual experience in adulthood. Kinsey devised a scale ranging from 0 (exclusively heterosexual) to 6 (exclusively homosexual) to measure this diversity of experience.

Well-conducted research indicates that homosexuality per se is not a sign of poor adjustment. Research does show somewhat elevated rates of depression and suicide among LGBs, which is almost certainly due to exposure to prejudice and hate crimes. Although some groups claim success in reparative therapy to change the sexual orientation of LGBs, there is no scientific evidence that one's sexual orientation can be changed and many indications that these therapies are psychologically harmful. Most therapists believe that it is extremely difficult to change a person's sexual orientation.

In regard to the causes of sexual orientation, biological explanations include genetic factors, hormone imbalance, prenatal factors, and brain factors. The genetic explanation has some support from the data, and there is new evidence of prenatal factors. Learning theorists stress that the sex drive is undifferentiated and is channeled, through experience, into heterosexuality or homosexuality. Bem's interactionist theory proposes that homosexuality results from the influence of biological factors on temperament, which in turn influences whether a child plays with boys or with girls; the less familiar (exotic) gender becomes associated with sexual arousal. Sociologists emphasize the importance of roles and labeling in understanding homosexuality. They also note that gender-rigid, male-dominant societies are likely to produce a higher incidence of gay men. Available data do not point to any single factor as a cause of homosexuality but instead suggest that there may be many types of homosexuality (homosexualities) with corresponding multiple causes.

Gay men and lesbians differ in some important ways. Women are more likely to be bisexual, and some theories that are effective in explaining men's sexual orientation are not supported for women.

Different ethnic groups in the United States, as well as different cultures around the world, hold diverse views of same-gender sexual behaviors.

Bisexuality has been overlooked both by researchers and by the general public. A person's sexual identity may be discordant with his or her actual behavior. Bisexuality may be more "natural" than either exclusive heterosexuality or exclusive homosexuality.