Among the consequences of nuclear fallout in the Cold War West was a new wave of fear concerning everyday existence and the future of human civilisation. In this chapter, the author examines the Danish debate over fallout by asking how knowledge about the effects of nuclear weapons was created, circulated, and contested. In the years following the bombings of Hiroshima and Nagasaki, Danish citizens had access to general knowledge and news reporting about the development of nuclear weapons technology. Alert to the devastation a nuclear war would entail and a fervent believer in a world federation, Professor Poul Brandt Rehberg grew into an “intellectual Cold Warrior”, who defended deterrence and represented an orthodox NATO position in Danish public debate. Especially Kampagnen mod Atomvabens emotionally charged campaign against nuclear weapons (testing) and for more information on the subject was discursively modelled on uncertainty and the long-term risks posited by geneticists.