A large part of environmental policy is based upon scientific studies ofthe likely health, safety, and ecological consequences of human actions and practices. These studies, however, are frequently vulnerable to epistemological and methodological criticisms which challenge their validity. Epistemological criticisms can be used in ethical and political philosophy arguments to challenge the applicability of scientific knowledge to environmental policy, and, in turn, to challenge the democratic basis of specific environmental policies themselves. Uncertainty arguments thus draw upon philosophy of science, epistemology, ethics, and political philosophy to establish conclusions of practical relevance to environmental quality. A theory of how and when uncertainty arguments ought to be given credence in environmental decision making requires an account of how scientific research ought to be integrated into environmental policy generally, plus an account of how public environmental policy is to be set in a democracy.