This article examines the policy responses of Canada, Sweden, and the United States to the discovery of dioxins in pulp mill effluents and paper products, with particular attention to the impact of science and the scientific community on national environmental standards. Important areas of policy divergence were found, despite considerable scientific consensus among environmental scientists in the three jurisdictions, as the potential force of shared causal knowledge was undermined by competing domestic interests and different institutional contexts for decision-making. This analysis challenges the emphasis of the epistemic community literature on the role of scientists in promoting policy convergence, underscoring the importance of the interaction of ideas, interest group politics, and institutions in public policy-making.