A terrible sin, a gift from the gods, a mental illness, a natural human variation―over the centuries people have defined homosexuality in all of these ways. Since the word homosexual was coined in 1869, many scientists in a variety of fields have sought to understand same-sex intimacy. Drawing on recent insights in biology and genetics, psychiatrist Francis Mondimore set out to explore the complex landscape of sexual orientation.

The result is A Natural History of Homosexuality, a generous work that synthesizes research in biology, history, psychology, and politics to explain how homosexuality has been understood and defined from ancient times until the present. Mondimore narrates tales of love and courage as well as discrimination and bigotry in settings as diverse as ancient Greece and Victorian England, early America and fin de siecle Vienna. He also tells fascinating stories about societies which accepted, incorporated, or institutionalized homosexuality into mainstream culture, stories illustrating that same-sex eroticism was often accepted as a normal aspect of human sexuality. In twentieth-century America, researchers first recognized that homosexuality might not be "pathological" when Alfred Kinsey and Evelyn Hooker conducted the first studies of sexuality not biased by preconceived notions of "normal" sexual behavior.

After exploring sexual development in the human fetus, Mondimore reviews current biological research into the nature of sexual orientation and examines recent scientific findings on the role of heredity and hormones, as well as Simon LeVay's 1991 brain studies. He then turns to a very important focus: on people and their individual experiences. He explores "what happens between childhood and adulthood in an individual that makes him or her come to identify himself or herself as having a sexual orientation." He also explains our current understanding of bisexuality and the transgender phenomena of transsexualism and transvestism.

Finally, Mondimore analyzes the circumstances of such prominent scandals as the anti-homosexual trials of Oscar Wilde and Philip von Eulenberg, and recounts the Nazi persecution of homosexuals during the Holocaust. This far-reaching discussion includes a description of the ex-gay ministries and reparative therapy as well as the Stonewall riots and AIDS, ending with the emergence of gay pride and community.