Between 1960 and 1966, French forces began to prove their nuclear weapon capabilities by conducting seventeen nuclear explosions in the Algerian Sahara. This dissertation pursues an international history of French nuclear ambitions and the resistance and the criticism that they faced at regional, international, and global scales. It does so by tracking radioactive debris from the French explosions—Saharan fallout—and the scientists, activists, diplomats, and other officials who tracked it during the 1960s. This methodology relies on declassified archives—from France, the United States, United Kingdom, Canada, and international organizations—produced for these purposes of nuclear surveillance. Concerns extended beyond the health effects of radiation exposure. The presence of Saharan fallout constellated transnational networks of scientists and technicians across African territories bordering the Algerian desert. It also bred criticism that French explosions violated African sovereignty and heightened geopolitical inequalities during an unprecedented era of decolonization. The French blasts coincided with the Algerian War (1954–62), continued after Algerian Independence, and intersected with decolonization struggles in neighboring African territories. At the same time, Saharan fallout illuminated processes of Cold War realignment shaped by concerns about radiation exposure and nuclear risk during a widening arms race. By examining convergences between political contestation and fallout trajectories, this dissertation shows that the international controversy created by the French explosions in Algeria exceeded debates about nuclear proliferation and nuclear deterrence. These first French blasts, and the threat of radioactive contamination that they imposed on many African territories, spurred participation in nuclear weapons governance by the continent’s new national leaders and their newly independent allies. This dissertation concludes by evaluating the importance of the Saharan nuclear sites, and ongoing discussions about environmental remediation and victim compensation, in Franco-Algerian relations today.