Some risk events, assessed as relatively minor by technical experts, can elicit strong public concerns and result in substantial impacts on society and the economy. This is especially true in cases involving low-level radiation exposure. Social amplification is a conceptual framework that seeks systematically to link technical assessments of health and safety impacts with assessments of individual and social risk perceptions and risk-related behaviors. Individuals and social groups can amplify (or in some cases, attenuate) risk as they process information about events, and events can produce secondary ripple effects that may spread far beyond the initial impact and may even affect unrelated technologies or institutions. Events that are highly dreaded, poorly understood, or both have high potential for these second-order effects. Social distrust of institutions and their managers plays an important part in amplifying risk. Understanding how trust is shaped, altered, lost, or rebuilt in the processing of risk by individuals and groups is a priority need in social amplification research. The social amplification of risk has become an essential part of an integrated assessment of risk. Recent changes in nuclear energy policy cannot be understood without serious examination of the social amplification and attenuation processes at work.