This dissertation examines the role of scientific and medical disciplines in the construction of homosexuality in Mexico, and how non-normative gender and sexual subjects engaged in political activism, body modifications, and aesthetic production to challenge the pathologizing discourses reinforced by the increasing authority of the biomedical sciences. Chapter 1 examines the role of photography as a medical instrument in the first documented sex-reassignment treatment in the Western Hemisphere performed by Mexican physician and sexologist Rafael Sandoval Camacho in the early 1950s, and how his patient Marta Olmos, Mexico’s first transsexual woman, embraced photojournalism as a medium to document, archive, and validate her identity as a woman. In chapter 2, I examine the popular phenomenon of publishing photographs of erotized trans sex workers known as Mujercitos during the 1970s in Alarma!, Mexico’s most influential crime tabloid magazine, and how these marginalized subjects appropriated biomedical technologies like “sex hormones” intended to regulate gender and sexual deviance to construct bodily identities that challenged the medical and criminological positions on the essentialist natures of gender expression, sexual desire, and the sexed body. Chapter 3 examines the early gay narrative of Luis Zapata and José Rafael Calva that emerged in conjunction to Mexico’s Homosexual Liberation Movement in the late 1970s. My analysis demonstrates how Zapata’s El vampiro de la colonia Roma [Adonis García: A Picaresque Novel] (1979), and Calva’s Utopía gay [Gay Utopia] (1983) present sharp critiques shared by Mexico’s homosexual liberation groups on the growing authority of disciplines like psychiatry, psychoanalysis, and biomedicine in pathologizing homosexuality. Chapter 4 examines the changing understandings of homosexuality, homosexual desire, and the homosexual body during the HIV/AIDS crisis through the work of Julio Galán, Nahum B. Zenil, and art collective Taller Documentación Visual. My analysis presents the role of the HIV virus not as an explicit visual reference but rather as an elusive, spectral, and dangerous entity that is identifiable through the aesthetic and formal composition of the artists’ works, best exemplified by the references to condoms as physical and symbolic devices in the mediation of gay sexual contact and desire. This dissertation demonstrates the critical roles of biomedicine, criminology, sexology, and psychiatry in regulating diverse forms of Mexican homosexualities, while simultaneously functioning as liminal disciplines strategically adopted by homosexual subjects to redefine, shape, and validate their desired bodily, sexual, and subjective identities.