In this special issue, contributors trace how sexual scientific thought circulated throughout the late nineteenth and twentieth centuries and how that thought continues to shape sexuality. The authors situate the science of sex within a broader context of sexuality studies, which examines the social, psychological, and political aspects of desires, acts, identities, and sexology. Articles-addressing topics such as early gender clinics and transsexual etiology, the taxonomy of queer identities, and blackness and sexology-examine the current and historical ways in which racial science and colonial knowledge constitute sexual science as an amorphous object, one with a problematically vast reach that buttresses racial hierarchy and undergirds colonial infrastructures. The authors urge readers to explore how the taxonomies of sexual science structure identitarian frameworks of gender and sexuality. Contributors: Kadji Amin, Howard Chiang, Stephanie D. Clare, Emmett Harsin Drager, Patrick R. Grzanka, Benjamin Kahan, Greta LaFleur, Rovel Sequeira, Aaron J. Stone, Zohar Weiman-Kelman, Joanna Wuest