--- - |2 Abstract Debates on risk have largely assumed risk to be the outcome of calculative practices. There is a related assumption that risk objects come only in one form, and that the reason not everything can be transformed into a risk is because of the difficulties in calculating and creating universal quantitative comparisons. In this article, building on recent studies of preparedness that have broadened understandings of risk, we provide an analysis of how preparedness measures might themselves produce risk, in particular through risk's durable instantiation, or what we call ‘concretization’. Our empirical focus is on how government agencies in two countries shifted their attention from the risk of nuclear attack during the Cold War to an all hazards approach to preparedness. Comparing the mid‐ to late‐twentieth century histories of the UK and Switzerland, we show that both countries shifted from focusing from a single risk to plural risks. This shift cannot be explained by a change in prevailing calculative practices, or by the fact that the risks changed historically. Instead, it is driven by historically specific changes in how risks are produced and reproduced in relation to how materializations of risk operate over time. - 'The British Journal of Sociology, Volume 69, Issue 3, Page 799-824, September 2018. '