AbstractDecision-making in Europe is conducted through extremely subtle and infinitely varied mechanisms. What is the part played by expert appraisal and scientific rationality? While the functioning of the Commission and the ‘economy’ of the system of European institutions have tended to favour confrontations between a multiplicity of expert appraisals, this pluralistic approach has not been sufficient to ensure the scientific rationality of decisions. Yet there have been positive, dynamic effects of European construction on the relations between science-politics-expertise at the level of the member states.