This article considers how the concept of risk has been variously defined and deployed within research and UK social policy since the 1980s. The article does not present an in-depth historical narrative, but rather presents key trends over this period. The article begins with a short review of policy and risk rationalities from the 1980s onwards with a specific focus on the research 'discovery' of the 'rationality mistake' by the early 1990s. A short case study from the author's own research is then presented to illustrate the 'rationality mistake' in a particular arena of UK government policy on the management of sexual offenders. The paper concludes by briefly considering actual and potential developments in risk research and relevant recent theorising, and finally the likelihood of social policy understanding the risk subject more fully.