The key to expanding the energy supply, increasing energy security, and reducing the dependency on foreign oil is to develop advanced technologies to efficiently transform our renewable bioresources into domestically produced bioenergy and bioproducts. Conventional biorefineries, i. e., forest products industry's pulp and paper mills with long history of sustainable utilization of lignocellulose ( wood), offer a suitable platform for being expanded into future integrated forest biorefineries. Due to the preexisting infrastructure in current forest products operations, this could present a very cost-effective approach to future biorefineries. In order to better understand the overall process, technical, economic, and environmental impacts, a detailed process modeling of the whole integrated forest biorefinery is presented here. This approach uses a combination of Aspen Plus (R), WinGEMS (R), and Microsoft Excel (R) to simulate the entire biorefinery in detail with sophisticated communication interface between the three simulations. Preliminary results for a simple case study of an integrated biorefinery show the feasibility of this approach. Further investigations, including additional details, more process options, and complete integration, are currently underway.