Recent developments in the acetone-butanol-ethanol (ABE) fermentation will be discussed with a focus on strategies for the development of second generation strains.  The ability of the solventogenic clostridia to utilize mixed sugar streams bodes well for the potential use of biomass for this fermentation.  Biomass pre-treatment and enzyme hydrolysis are known to result in the formation of degradation products that may inhibit microbial growth and fermentation.  Approaches to overcome this limitation and scale-up of the integrated system for production of bio-butanol will be discussed.