Researchers will review the state of the art of modeling the physical behavior of granular materials. They will focus on the limitations of existing models and explore how they may be extended. The participants will be invited to present the derivation of the models, to describe the existing physical and numerical experiments, and to discuss what features of the experiments the model can and cannot predict. Discussions will address issues raised by the speakers, attempt to clarify them, and indicate how their resolution might advance the subject.