The technological risks associated with electricity generating options are a crucial consideration in the governance of energy strategies. Conversely, many central issues in the broader social debate over the governance of environmental risk (such as acid gas emissions, radioactive waste management, nuclear safety and global climate change) relate very strongly to technology choice in the electricity supply sector. The particularities of this field, therefore, offer a topical and pertinent case with which to explore the relationship between science and precaution in the governance of technological risk. By reference to the electricity sector, the present paper examines the contrasts between 'risk-based' and 'precautionary' approaches to the governance of risk, paying particular attention to the problems of intractable uncertainties and divergent values. A number of theoretical and methodological issues in conventional risk-assessment and cost-benefit analysis are examined and their practical implications for appraisal explored. Attention then turns to the form that might be taken by approaches to the governance of energy risks that are at the same time scientifically well-founded and precautionary. Conclusions are drawn for decision and policy making in this area.