This paper analyses the failure of the introduction of GM crops in Europe. It challenges the idea that this failure is due to the influence of the public irrationality on decision processes. Instead, it focuses on the inability of the regulatory system to manage complex situations which result from the limits of sound science in contexts of uncertainty and controversy. It argues that the way out of the currently blocked situation requires more open and participatory processes of innovation and technological assessment, based on the normative stance provided by the precautionary principle.