One principal barrier to economic utilization of lignocellulosic feedstocks in enzymatic systems for the production of alcohol fuels is a cost-effective pretreatment. The objective of a pretreatment is to render the cellulose susceptible to enzymatic hydrolysis. The lignin and hemicellulose fractions need to be partially or totally removed to enhance the hydrolysis. This report presents a detailed discussion of the physiochemical characteristics of lignocellulosics that must be considered it the development of successful pretreatment. Engineering and economic assessments are presented for key pretreatments based on organic solvent extraction (organosolv), explosive decompression (steam explosion), and wet oxidation. These assessments include process flowsheets, capital and operating cost summaries, and parametric analyses comparing the effects of various raw material and utility costs. Based on the cost of cellulose pulp produced, these pretreatments are competitive with pulping processes currently used in the paper industry. The pretreatment and feedstock costs contribute a significant amount--over 50% in most cases--of the cost of ethanol production. Recommendations are presented for a program of process-specific and integrated pretreatment-hydrolysis research.