The Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) was formed in 1999 as a multi-institutional effort to develop comparative information on cellulosic biomass pretreatment options. Initial work focused on a comparative evaluation of corn stover feedstock for five leading pretreatment technologies (dilute acid, hot water, ammonia recycle percolation, ammonia fiber explosion and lime). More recently completed efforts, known as the CAFI 2 project, included both corn stover and hybrid poplar as feedstocks on which performance data has been collected. Also, an additional pretreatment approach (SO2 pretreatment), has been included in the research and process modeling aspects of the CAFI 2 project. Process modeling updates include the use of a more current costing basis for the economic models, the development of a graphical user interface, and the incorporation of a woody biomass feedstock handling system that is suitable for handling the hybrid poplar feedstock. The final pretreatment, enzymatic saccharification, and hydrolyzate fermentation data on corn stover and hybrid poplar for each pretreatment process has been incorporated into the economic models. Model scenarios that project a Minimum Ethanol Selling Price (MESP) for a “current” technology case (based upon available bench-scale data) and a “target” case (based upon reasonable projections of improved, commercial-scale performance) have been developed for each pretreatment process for both corn stover and hybrid poplar.