Growing concerns over the variability of oil prices, energy security, and the impact of global climate change provide impetus to transform plant biomass, on an industrial scale, to renewable liquid transportation fuels with a low carbon footprint.  Facile transformation of solid cellulosic substrates to biofuels through yeast or bacterial fermentations is now possible.  The enabling biotechnology is based on concerted research to transform, amplify and / or combine cellulolytic and fermentative pathways in pentose fermenting yeast and bacteria.  Leading feedstock pretreatments, several of which require little or no chemical addition, result in woody biomass and agricultural cellulose that is sufficiently reactive to serve as the substrates for industrially relevant cellulolytic microorganisms that ferment both hexoses and pentoses to alcohols.  A final challenge remains – scale.   Economical, industrial fermenters for pretreated, high solid slurries are needed to move this technology from the laboratory to the highway.  Fundamentals of fermenter characteristics for handling cellulose slurries to achieve fermentation rates, titers, and yields associated with a commercially viable process will be discussed.  We present work from a team effort that is combining science and engineering to achieve commercially viable fermentation of cellulose to ethanol via consolidated bioprocessing.