The aim of this article is to analyse the role of science in environmental regimes. The focus is on through which conceptual lenses social scientists should judge the role of science in this area. In answering this question, the article takes as its point of departure the sociology of scientific knowledge (SSK). Three key findings of SSK are central to understanding the role of science in environmental regimes, namely that knowledge never moves freely, that the value of science is the result of negotiations and that science and policy are co-produced. The usefulness and explanatory power of this perspective is illustrated by a case study of one of the most science-based regimes that exist today, the Convention on Long-Range Transboundary Air Pollution (LRTAP). By way of conclusion, it is stated that science has no strength in itself but is given strength by different institutions and actors, and this has to be explained by social scientists.