The Policy Analysis System (POLYSYS) is a national simulation model of the US agriculture sector which can incorporate agricultural supply and demand and related modules to estimate agricultural production response, resource use, price, income, and environmental impacts of projected changes from an agricultural baseline. The framework recursively incorporates linear programming, econometric, and process models to estimate an impact path resulting from changes imposed on a baseline scenario and its underlying assumptions. POLYSYS estimates crop production and supply at a disaggregated regional level, whereby the 48 contiguous states are subdivided into 305 geographic regions with relatively homogeneous production characteristics. POLYSYS is capable of estimating a wide range of policy alternatives and economic and environmental conditions and simulations may be tailored to a variety of specific analytical needs. This paper presents a broad overview of the structure and approach of the POLYSYS model with emphasis on biomass and bioenergy related applications of the model. © 2000 Elsevier Science Ltd.