This paper explores the influence of English female doctors on the creation of the International Planned Parenthood Federation (IPPF) and the production and circulation of contraceptive knowledge in England and, to a lesser extent in France, between 1930 and 1970. By drawing on the writings of female doctors and proceedings of international conferences as well as the archives of the British Medical Women’s Federation (MWF) and Family Planning Association (FPA), on the one hand, and Mouvement Français pour le Planning Familial (MFPF), on the other, this paper explores the agency of English female doctors at the national and transnational level. I recover their pioneering work and argue that they were pivotal in legitimising family planning within medical circles. I then turn to their influence on French doctors after World War II. Not only were English medical women active and experienced agents in the family planning movement in England; they also represented a conduit of information and training crucial for French doctors. Transfer of knowledge across the channel was thus a decisive tool for implementing family planning services in France.