Pretreatment is essential to high yields and low costs for biological processing of cellulosic biomass to fuels and chemicals.  A team experienced in biomass hydrolysis formed a Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) to develop the first comparative data for the promising pretreatment options of ammonia expansion, aqueous ammonia recycle, controlled pH, dilute acid, flowthrough, lime, and sulfur dioxide steam explosion.  Corn stover was initially employed, and material balances were developed based on use of shared analytical methods.  In addition, comparative data were developed on the digestibility of the pretreated solids using a controlled source of cellulase.  All pretreatments were effective in making cellulose accessible to enzymes with high yields, with trends slightly better for high pH technologies.  Xylose recovery yields were high for all these pretreatments, although hemicellulase activity was vital to recover the substantial amounts of xylan left in the residual solids for pretreatments at high pH.  However, yields were much more variable for applications of the same technologies to poplar wood, and significant performance differences were observed among these pretreatments for different poplar species.  The fermentability of the pretreated hydrolyzates and solids with a recombinant yeast strain was also assessed, with some requiring more conditioning than others to realize good ethanol yields.  Finally, material and energy balances were developed based on this data and used to project the impact of each pretreatment on the minimum ethanol selling price.  Overall, these results show the importance of linking selection of pretreatment technology with feedstock choice.