Large-scale modeling systems have long been viewed as potentially valuable tools for evaluating farm policy. They have received increased attention in recent years, in part because of the added complexity of U.S. farm programs and the fuller integration of the U.S. farm sector with nonfarm sectors and world agricultural commodity markets. Instability in the world economy, changed macroeconomic policies, credit and debt positions, and agricultural trade regulations have significant impacts on U.S. agriculture in the short run and more pronounced long-run implications. It is important that policy models explicitly address these complexities of agriculture if they are to be successfully applied in policy design and evaluation.