Decentralization of renewable resource management provides an opportunity for local stakeholders to increase their participation in decisions affecting them. Research should propose adapted methodologies and tools enabling the numerous stakeholders of complex socio-ecosystems to identify and discuss about possible solutions to their common problems. We show that in participatory modelling processes, simple models can be as useful as comprehensive and sophisticated ones to accommodate multiple interests among stakeholders, on the condition that the modelling and simulating process itself is carefully participatory, i.e. pays much attention to the initial socio-political context in which this participatory modelling process takes place to ensure the genuine participation of all concerned stakeholders (including the usually voiceless and ressource-poor ones). This assumption is discussed by drawing on a Companion Modelling (ComMod) experiment on water management in a Northern Thailand highland community. The basic principle of the ComMod approach is to develop simple simulation models integrating different stakeholders¿ points of view on the problem at stake, and to use them in communication platforms to explore and discuss collectively various scenarios for the future. By combining a preliminary analysis of the heterogeneous socio-political context with a very simple Agent-Based Model, a Role-Playing Game, individual interviews, and group debates, this ComMod process was efficient at stimulating collective learning and coordination among multiple stakeholders exploring pathways to solve their common water use problem.