Linking modeling tools and the participatory approach for development is not a common combination. Participatory multi-agent system modeling (PMASM) is a tool for sharing viewpoints among stakeholders and facilitating the negotiation process. A key question of this approach is the acquisition and the modeling of the various stakeholders' representations. Our research team, whose Asian branch is represented in this book, tries to formalize the passage from fieldwork to the model by defining a methodology that can be implemented in the field. This methodology adapts knowledge engineering acquisition techniques to in-field stakeholders' representations for PMASM. In a northern Thailand watershed, we pursued implementation tests of this methodology. We first explored two ways to tackle fieldwork (ethnographic and project surveys), both showing weaknesses and strengths. We then built a first-version diagram syntax used for representing individual farmers' representations, and we considered options for analyzing those diagrams. Finally, we tested the elicited representations by leading farmers, through game-like sessions, to rebuild a model of their system structured by elements and links. Results reveal a great heterogeneity of farmers' representations, which we intend to manage by establishing farmers' synthetic profiles based on their orientations toward specific elements and aspects of their social and natural environment. Orientations of those profiles convey different conceptions of the functioning of the system with which farmers interact. This also results in decisions and reactions to issues that are different from one profile to another. The identification and formalization will contribute to the implementation of a computer model of farmers' representations. Perspectives are drawn on two ways to integrate representations into the modeling.