Why are sports segregated by gender? Why do women play some sports and not others? What makes gymnastics a feminine sport? Why shouldn’t men compete in synchronised swimming? Why didn’t women compete in Olympic weightlifting before 2000? These questions have gained renewed prominence in the wake of South African athlete Caster Semenya’s legal appeals against the decision by the International Association of Athletics Federations to reduce her testosterone levels, the ‘me too’ movement, revelations of years of abuse in women’s gymnastics, and the controversies around Laurel Hubbard’s transition from male to female and what it meant for her weightlifting career. These issues have cast a fresh spotlight on the gendering of sport which has created barriers to discrimination against women, and a range of psychological and health problems for women, especially young women. This project employs historical sociology to understand how sports’ international governing bodies create, enforce, and dismantle gender segregation. It uses gymnastics, swimming, and weightlifting as case studies to compare how three sports have been engendered through their international federations’ rules and policies. Immersion in historical archives combined with qualitative interviews provide the data for the project, which will be analysed using a gender theory. In doing so, this project aims to provide a critical understanding of the binary gendering of sports as masculine or feminine, and offer new policy recommendations for sports associations to achieve greater inclusivity in sport. It will also expand the scientific skills of the researcher by incorporating sociological theory into history. It thereby broadens her expertise and reinforces a mature research position, improving the fellow’s employability post-project.