Protest against nuclear power plants, uranium mining and nuclear testing played a pivotal role in the rise of a mass environmental movement around the globe in the 1970s and 1980s. Nevertheless, the history of anti-nuclear activism has largely been told from a strictly national perspective. This HSR Focus approaches the phenomenon from a transnational perspective for the first time. Against the backdrop of the debate on transnational history, this article develops a framework of analysis, and contextualizes anti-nuclear protest in a broader postwar perspective. The contributions show that anti-nuclear movements across the globe were transnationally connected. First, scientific expertise and protest practices were transferred between movements, and subsequently adapted to local requirements. Secondly, transnational cooperation and networks did indeed emerge, playing an important role in taking protest to the international and European level. However, as opposed to contemporary rhetoric of grass-roots transnational solidarity, such cooperation was limited to a small, highly skilled and committed group of mediators – often semi-professional activists – who managed to overcome the obstacles of distance and cultural differences and had access to the necessary resources.