Participation and transdisciplinarity have become “mantras” when dealing with agrifood systems transitions. However, both are considered in very diverse ways and there is a need to discuss and assess the conditions for them to be truly beneficial to support transition processes and the inclusion of the people who are firstly concerned by these processes, in their actual social diversity. This collective reflexion is based on the action research experiences of the co-authors dealing with agroecological transitions at the scale of territorial food systems in different contexts (France, Belgium and the UK, in both urban and rural regions) as well as on a cross-discussion of their previous writings about transdisciplinarity that took place within the ATTER European project. This collective reflexive work on our transdisciplinary thinking and practices – especially that of creating devoted arenas of debate for inclusive processes of knowledge building and transition pathways’ designing - will lead us to discuss three key issues: -What role for local actors in defining collective understandings of territorial food system trajectories? How to come to a “shared problem” definition in territorial food system transition, beyond research extractivism or/and the exclusion of concerned segments of the local population? -What meaningful role for concerned actors – and not only “stakeholders” - in the relevant arenas of debate, in a context where generic tools and methods as well as multi-stakeholderism increasingly frame participation? -How may the diversity of visions of ecologisation, which is usually “reduced” to the diversity of actors and/or framed in such a way as to reduce the gaps between these visions, be invited into the arenas of food system transition debate? How to bring this diversity back to the foreground, and value it as a shared object so that it plays in favour of socially just transition processes? Finally, and as a transversal issue, we will discuss the specificity of rural as opposed to urban contexts and the need to adapt action research postures according to the contexts.