The dissertation examines the influence exerted by government\u27s own experts, particularly natural, social and applied scientists, in the making of environmental policy. It focuses on the priorities for environmental policy, rather than the policies themselves, and addresses the question of how and under what conditions expertise resonates within environmental priority setting. The research involved an extended case study within Environment Canada, between the years 1992 and 1995. In particular, it examined the Environment Canada Project Plan as it moved through its various stages of development, implementation and finally, failure to be approved. It examined other projects also proposed and possibly implemented during the same time period. Based on an extensive collection of documents, including internal departmental memos provided to this research, interviews and participant observation, it was observed that government experts were not always influential even in situations where the professed method of policy making was "science-based." The readily available government experts were not always asked for their advice, nor were they always listened to even when they were asked. A great deal of expert influence, or lack of influence, can be accounted for by serendipity, the effect of particular individuals in particular positions at particular moments in time. The overall conclusion of the research is that, despite adherence to the value of "science-based" decision-making, policy making (at least in this instance) was not science-based in any significant measure. Even in the setting of priorities for attention, and even in the field of the environment, policy making remains mainly responsive to factors other than science. The dissertation concludes by suggesting that greater emphasis on "sciencebased" policy making might go some distance to redressing the lack of influence of government experts. The discussion of specific policies might also be widened to allow people other than government officials to participate. It may well be that more attention to the contribution of experts might occur were the public involved in pressing for "science-based" policy