Although Havelock Ellis wrote on a variety of subjects, he was most famous, or notorious, as the preeminent sex theorist of his era in Britain. He discussed sex and promoted birth control at a time when neither of these activities was done openly. A pioneering sexologist, Ellis argued that women should enjoy their sex lives, and he was unusually tolerant of "deviant" sexuality. He was the first English-language writer to report sympathetically on homosexuality and lesbianism, or "sexual inversion." A self-described socialist, Ellis was also loosely connected to other progressive and radical movements of his time.

His interest in sexuality was rooted in his own sexual problems and his attempts to wrestle with them. It is believed that Ellis never completed sexual intercourse, either with a woman or a man, and Phyllis Grosskurth notes that the subjects of penetration and male orgasm are curiously missing from his sexual...