This thesis is based on the assumption that the intersection of moral philosophy and practical risk management is a rewarding area to study. In particular, the thesis assumes that concepts, ideas, and methods that are used in moral philosophy can be of great benefit for risk analysis, but also that practices in risk regulation provide a useful testing ground for moral philosophical theories. The thesis consists of an introduction and five articles. Article I is a review article on social and ethical aspects of radiation protection related to nuclear power generation. The paper concludes that four areas of social and ethical issues stand out as central: The first is uncertainty and the influence of value judgments in scientific risk assessments. The second is the distributions of risks and benefits between different individuals, in both space and time. The third is the problem of setting limits when there is no known level of exposure associated with a zero risk. The fourth is related to stakeholder influence and risk communication. Article II discusses ethical issues related to the proposal that doses (or risks) below a certain level should be excluded from the system of radiation protection, without any regard for the number of people exposed. Different arguments for excluding small radiation doses from regulation are examined and a possible solution to the problem of regulating small risks is proposed in the article: Any exclusion of small doses (or risks) from radiation protection ought to be based on a case-by-case basis, with the condition that the expected value of harm remains small. Article III examines what makes one distribution of individual doses better than another distribution. The article introduces a mathematical framework based on preference logic, in which such assessments can be made precisely in terms of comparisons between alternative distributions of individual doses. Principles of radiation protection and from parallel discussions in moral philosophy and welfare economics are defined using this framework and their formal properties analyzed. Article IV argues that the ethical theory of “responsibility-catering prioritarianism” is well positioned to deal with the reasonable requirements in an ethical theory of risk. The article shows how responsibility-catering prioritarianism can be operationalized using a prioritarian social welfare function based on hypothetical utilities. For this purpose, a hypothetical utility measure called ‘responsibility-adjusted utility’ is proposed, which is based on the utility that would normally be expected given circumstances outside of the control of the individual. Article V was written as a response to the Fukushima disaster. Several authors have called the Fukushima disaster a ‘black swan.’ However, the article argues that the hazards of large earthquakes and tsunamis were known before the accident, and introduces and defines the concept of a ‘black elephant,’ as (i) a high-impact event that (ii) lies beyond the realm of regular expectations, but (iii) is ignored despite existing evidence. / QC 20120816