Participative approaches are often viewed as an interesting way to promote the links between local and regional levels necessary to policy decentralization. Among those, the companion modelling (ComMod) approach aims at developing collective learning and at supporting decision making process by eliciting the different perceptions of a complex situation and by collectively exploring possible futures. This participative modelling and simulation approach has historically been developed and experimented at local level. But as many participative approaches, it has rapidly been confronted with the questions raised by the necessary inclusion of larger scale of decision. For instance, to which extend is it possible to transfer the collective knowledge developed to non-participants, or how to associate different types of stakeholders such as regulators? This institutionalisation of the approach implies up-scaling processes (transfer of the approach to higher decision levels), as well as out-scaling processes (dissemination of the approach and outputs to actors of the same level than the participants). When considering the link between human and environment processes, it is now widely acknowledged that scales are social and political construct and that the organisation in level of the society is subjective. Furthermore, the perception of the dimensions to be accounted for varies from one actor to the other. Thus, according to the participation strategy, the issue definition, the representation process, the tools legitimacy and the mode of integration and comprehension of knowledge may differ. This paper presents and discusses methodological strategies that have been tested in 14 experiences to institutionalise the ComMod approach. Participation, representation development and implementation methods, such as: participation of external actors at various moments of the approach, specific communication methods, development of generic tools and representations, training and format