Dynamic modelling is a frequently used approach for solving problems in interorganizational systems. In order to construct valid models of such systems, representatives of the individual organizations must be involved in the modelling process. Current approaches of dynamic modelling use a form of 'consultative design' for handling the participation of organizational representatives. Based on findings in literature on participatory design and on previous research on the design of interorganizational information systems, we claim that a more 'participative' dynamic modelling approach for modelling interorganizational systems would be appropriate. This paper presents a model-framework for 'multimodels', and a participative approach for building such models.