Résumé : During the 2nd Indochina War (1956-1975), the United States Airforce made use of a set of herbicides and defoliants on the former Republic of Vietnam, through a mission named Ranch Hand. The most commonly used product was Agent Orange, named after the orange band marking its containers. Produced by American agrochemical companies (among which Dow Chemical and Monsanto – now Bayer), under the request of the United States government, the Rainbow Herbicides, as they were called, were considered to be only harmful to plants, and safe to human beings. Through a transnational study study of scientific research, legal activism, NGO work and policy making, and using a Science and Technology Studies lens, this research highlights the process through which Agent Orange's use and/or innocuousness has been contested.