There is a notable lack of scientific consensus on whether electric and magnetic fields (EMF) constitute a health risk in need of systematic control. Even those who see EMF as a public problem, share few assumptions about the type of problem it represents, whether serious risks to health are involved, or about the collective action it warrants. In the absence of conclusive scientific evidence, the interpretations of various social and political institutions have moved into the foreground, each bringing a different perspective to the issue and a unique way of accommodating the ambiguity surrounding the question of health effects. The result is a confusing mixture of warnings and reassurances, of calls for more study, or for immediate action, that distinguishes the EMF issue from other, better-defined environmental risks. While much of the discussion of EMF has focused on the synthesis and assessment of experimental and epidemiologic research on health effects, this paper explores the diversity of institutional interpretations to shed some light on the social and political responses to the issue and how these might shape its future in public policy. The paper concentrates on the selected norms and practices of three institutions, centrally involved yet differing in their interpretations: the scientific community, the legal system, and public bureaucracy. The disparities that form among the interpretations of institutions faced with ambiguous evidence and ill-formed problem definitions can lead to tensions and a search for alternative means of resolving contested meanings.