As concepts that differ across history and between cultures—even diverging radically within a single time and place—sex, gender, and desire are most accurately understood when examined through a historically and culturally specific lens. This thesis directs that lens towards the intersection of sexology and art in early-twentieth-century France with a specific interest in representations of the third-sex subject in visual culture. Classified as neither women nor men by sexologists, members of the third sex at the turn of the twentieth century occupied a turbulent middle-ground between masculinity and femininity, and defied sexual and romantic social norms. Early sexology produced a plethora of images to serve as evidence of the innate nature of sexual desire and gender identity, and queer artists consuming sexologists’ work responded in kind with artistic works that grappled with theories of gender and sexual identity. This study deepens art historical engagement with images that contributed to and were influenced by sexology discourse in the early-twentieth century; artists like Romaine Brooks, Berenice Abbott, and Claude Cahun negotiated sexological theories about sex and gender in artworks that challenge binary conceptions of identity and make visible the third-sex subject.