The Integrated Dynamic Energy Analysis (IDEAS) model is a simulation model designed for long-term policy analysis of the U.S. energy system. The U.S. Department of Energy for over two decades has used it to evaluate potential legislation and long-term strategies. The model emphasizes the interaction among the various energy sectors, which is important because policies in one sector often have consequences for others. Its quick running time and flexibility mean that IDEAS is ideal for what-if policy questions where multiple scenarios are to be analyzed. The model has been used for several national energy policy plans and more recently for environmental analyses. For example, IDEAS was the integrating modeling framework for the 1993 Climate Change Action Plan and its update in 1997. OnLocation provides the primary support to DOE for the IDEAS model.