This dissertation addresses one of the most popular management control practices adopted worldwide over the last three decades: the practice of risk management. The current risk management literature has argued that our knowledge of the particularities of risk management practices is limited. It has been stressed that knowledge is particularly lacking about the long-term effects of practising risk management. This dissertation responds to these calls by carrying out two longitudinal case studies of two large Danish public capital investment programmes, also known as mega-projects. The focus of the two studies has been on three key risk management-related aspects: (1) the translation of uncertainties into risks, (2) the relationship between frameworks and practices of risk management, and (3) the effects of practising risk management on knowledge and project management roles. The dissertation further advances current risk management literature into the study of mega-projects and draws upon actor-network theory. It consists of three papers, which each deals with one of the above aspects. The dissertation presents three major findings. Firstly, it is demonstrated that, contrary to expectations, only some types of uncertainties are included as risks, termed pure risks, while others, termed impure risks, are systematically excluded despite the finding that people found them relevant to include. This finding is explained with reference to technical risk devices as these were found to define the boundaries between what can and what cannot be defined as an acceptable risk and thus be included. Secondly, the dissertation demonstrates that by enacting certain realities of ‘risk’ and ‘risk management’, frameworks of risk management make the practice produce the risks that confirm its propositions and thus its success. In addition, the dissertation shows that when provisional situations arise which undermine the frameworks’ propositions, reconfiguring the risk management control system, risk terminologies and the roles of actors become key actions performed to re-establish the practice. Lastly, the dissertation demonstrates that during project processes, new uncertainties emerge which challenge project and risk management objectives as new knowledge about the conditions is produced that cannot be included. In sum, this dissertation contributes by shedding light on how practices of risk management are constructed and the effects they produce over longer periods of time.