Since 1996 France has had an intensified public controversy about the commercialisation of GM crops. As new actors have entered the debate and raised new issues with the experts, the uncertainties (related to agronomic, environmental and human health consequences) have tended to increase and the previous standards of precaution have been challenged as inadequate. In response, the French government has begun to open up the regulatory process in order to involve citizens, NGOs and scientists within the official expert structures. Thus the French public controversy becomes a space where plant biotechnology is subjected to a social assessment. This article attempts to analyse some consequences of the introduction of the precautionary principle into the public decision and the scientific expertise.