International audienceThis article analyzes learning processes resulting from the collective construction of a transdisciplinary research project, and from the implementation of a participatory approach to agricultural non-point source pollutions (nitrates and pesticides). The study is based on a participatory research project carried out in the Brie plain of Seine-et-Marne (France). It is regarded as a border-crossing process across disciplinary boundaries which often arbitrarily oppose researchers and stakeholders, as well as dividing the different stakeholders concerned by a public issue. The analysis first examines learnings resulting from a preliminary stage of participation co-engineering that involve scientists and their socio-profes...