He was the initiator and is the director of OutHistory.org, a site devoted to lesbian, gay, bisexual, transgender, queer, (LGBTQ) and heterosexual history, that went online in September 2008, and was produced in its first four years by the Center for Lesbian and Gay Studies, an institute at the City University of New York Graduate Center, under a grant from the Arcus Foundation.

In 2003, he was given Yale University's Brudner Prize, an annual honor recognizing scholarly contributions in the field of lesbian and gay studies.

In 1975, the book series, Homosexuality: Lesbians and Gay Men in Society, History, and Literature: Documents of the Homosexual Rights Movement in Germany, 1836-1927 (Arno Press), which he edited received the American Library Association's Gay Book Award, a "grassroots acknowledgment honoring hallmark works in GLBT publishing".

Coined in 1868 (in German, Heterosexualität) by Karl Heinrich Ulrichs, the term initially referred to a person with an overwhelming drive toward the opposite sex and was associated with a number of pathologized behaviors.

Krafft-Ebing's Psychopathia Sexualis, published in 1889, and then in English in 1892, marked the clear turning point from a procreation-based sexuality to a pleasure-based ethic which focused on a "different-sex"/"same-sex" distinction to define the normal and the abnormal.

One of the important consequences of this line of thought which Katz notes in "Homosexual" and "Heterosexual": Questioning the Terms, is that projecting present sexual and gender categories on the past is with a limited degree of accuracy: "So profound is the historically specific character of sexual behavior that only with the loosest accuracy can we speak of sodomy in the early colonies and 'sodomy' in present-day New York as 'the same thing.'