"Flood control" policies have now shifted to "integrated flood risk management", which should also blend nicely within "water management" and "sustainable development". Thus, flood risk reduction strategies are one element to define in coordination with others in a broader picture. From a practical point of view, the relevance of flood management projects must now be examined under several angles. This is where Multi-Criteria Analysis is useful: they assess objectively the impact of projects through different indicators, either to guide decision-making by the project manager, or even to obtain final authorizations and/or funding. Here, we advocate that it could be used as guidance throughout all the stages of the project, to ensure informed decisions at each step, from the definition of the project broad lines to the choices of technical details. We propose here a practical method to define the best compromise between the different disciplines involved by the project, and all along the process. The idea is to make the best use of the competences of each involved person, including technical staffs. Co-conception implies the active participation of all. Therefore, our approach insists that first the objectives have to be explicit and shared, and that solutions must be found to discuss and compare the means of action, using common conceptual and operational views. Our approach still has to be implemented for full-scale studies, in real and varied contexts, to test and improve the method to a fully operational stage. Only then can "guidelines' be written, but always allowing much freedom in the implementation. Future implementations should be followed closely, certainly not to control the process, but to capitalize on the experience. Social sciences should be closely associated to the project, to analyze the paths towards solutions: how different specialists collaborate, which were the expected and unexpected misunderstandings at the beginning, how they were identified and solved, how compromises were made, how each specialist around the table really influenced the final version of the project. Of course, each project is different, but feed-back analysis can always bring insight to the delicate art of project management and help identify obstacles and solutions for fruitful co-conception.