In this paper a theory of group facilitation and communication is introduced, based on the work of Gregory Bateson and the Palo Alto schools he founded and inspired. This theory permits an analysis of group facilitation processes on the basis of the same principles that inform system dynamic model building and simulation. Through this theory existing lists of appropriate facilitation skills and attitudes are elaborated and augmented. This leads to greater insight into the quality of the process of group model building and possible ways to evaluate that process. Ultimately, the growth and proliferation of system dynamic models and simulations depends on improvement of both process and content of modeling and simulation.