Group model building is nascent the latest years. However, only few educational institutions offer professional education and research in the field. Furthermore, detailed empirical literature about group model building is rather rare. Hence, this paper will serve three purposes connected to group model building. First, it will document and critically reflect upon a group model session and derive lessons learned. Second, it will create a comprehensive group model building framework based on existing streams of research. The result is a framework that includes context and stakeholder analysis as basic preparation tools for a group model building project. In the more modeling session oriented stages, the approaches of Vennix and Andersen et al. will be integrated. And thirdly, it will apply the developed framework to a current research project in which the diffusion of energy-efficient innovations will be modeled. Further research will concentrate on validation and elaboration of the developed framework.