Public perception of environmental and health risks is often quite different from that of the best experts, and is heterogeneous among the population. Maybe because of a lack of credibility, public authorities do not seem to be able to reach any consensus, nor to reconcile quite disparate arguments. In our works (see, in particular, Salanié and Treich, 2003), we argue that the existence of divergent perceptions, or disagreements, is a fundamental aspect of the risks. This leads us to study, from our viewpoint of environmental economists, the impact that these disagreements may have on public policies.