Abstract. If the precautionary principle is to become the guide of the international community for environmental protection policies, an economic interpretation of the principle is in order. The analysis of case studies and a survey of the recent decision theoretic literature show the lack of a fully satisfactory economic model. More generally various theoretical and empirical results show that the principle cannot be assumed to apply a priori. Though it has been proposed by international treaties as a rule of thumb for situations of scientific uncertainty, the precautionary principle could actually be inefficient.