Metropolitan areas have come under intense pressure to respond to federal mandates to link planning of land use, transportation, and environmental quality; and from citizen concerns about managing the side effects of growth such as sprawl, congestion, housing affordability, and loss of open space. The planning models used by metropolitan planning organizations were generally not designed to address these issues, creating a gap in the ability of planners to systematically assess them. UrbanSim is a new model system that was developed to respond to these emerging requirements and has now been applied in three metropolitan areas. This article describes the model system and its application to Eugene-Springfield, Oregon.