This paper introduces cognitive negotiation support which is based on the restructurable modeling approach. Cognitive support systems allow for the integration of qualitative and quantitative representations, support basic approaches to decision making, and provide descriptions of alternative realities. The development of representations and the process of their modifications are illustrated with Canada-U.S. Softwood Lumber Negotiations. Several experiments were conducted to show the flexibility and expressive power of restructurable modeling and its computer implementation, the Negoplan system. The approach allows for the stability analysis of alternative proposals and use of different prescriptive methods and descriptive models for a more comprehensive simulation and analysis of negotiation processes.