The collective expression of attitudes towards energy systems governs demand and hence cost, which combines with other factors to shape energy policy. For example, in the national debate over nuclear power, where decision makers either share the public's anxieties about costs and safety or are expediently responsive to them, there is a constant threat to political acceptance. The paper describes how perceived risks are one of the costs of all technologies and a brief summary is made of research on comparative risk perception. This confirms the wide disparities often observed between lay and expert risk assessments and provides some explanations. When attention is focussed on particular hazards, the concept of attitude becomes more appropriate than risk perception because choice behaviour is determined by overall evaluations and these are a trade off between perceived risks and benefits. Each of the latter is acquired from two overlapping classes of received knowledge, i.e. factual information (e.g. nuclear power comes from the fission of uranium atoms), and beliefs (e.g. nuclear power will create/reduce employment). In addition, the attitude acquires emotional associations and behavioural dispositions, forming an organised complex based on the environmental object. This structural approach facilities the “unpacking” of public attitudes towards energy systems into their constituents and this is essential for understanding, for consultation and for inducing attitude change.