Résumé
To study the social organisation of sets of agents managing common property goods, we use multi-agent simulations. This paper describes how the idea of group is analysed in this context. On the one hand agents build constantly themselves and the community, through their actions on their common environment and their different interactions with others. On the other hand the group preexists to the agents and compels their actions. To move beyond this dualism we explore different ways to take in account both organisation levels at a same time. Two approaches of that idea have been implemented and are presented here. The first, modelling the potlatch, deals with emerging collective structures that are observed by the model user and by the agents themselves. The second, simulating irrigated systems, defines both organisation levels as autonomous agents that coevolve in their environment. A tool was specially created to stick together these two approaches and is described in the discussion.