Regulatory science is a set of knowledge standards that is influenced by both academic research, and the knowledge needs of regulatory actors. It has taken shape in stable, rather closed, circles of interactions between selected academics, industries and public agencies. Regulatory science is also, however, the object of public criticism and controversy that extend beyond these circles. The toxicity testing of pesticides, for instance, has become the object of critical judicial decisions, and is decried by environmental activists as much as by environmental or health academic scientists, and indeed now covered by certain professional media titles. This criticism both signals the existence of, and offers the opportunity to study, what one may call the ecology of regulatory knowledge, namely the fact that regulatory knowledge is virtually produced in a variety of fields - industrial, academic, social movements - the interactions of which it is necessary to analyse, to understand how a regulatory ‘science’, with its particular standards of knowledge and forms of authority, are taking shape or, on the contrary, fail to stabilize. The talk will describe this ecological perspective further, and illustrate how it can be put to use on the subject of pesticides regulation in Europe.