The renewed interests in clostridial acetone-butanol-ethanol (ABE) fermentation as a next-generation biofuel source led to significantly intensified research in the past few years. This mini-review focuses on the current status of metabolic engineering techniques available for the model organism of ABE fermentation, Clostridium acetobutylicum. A comprehensive survey of various application examples covers two general issues related to both basic and applied research questions: (i) how to improve biofuel production and (ii) what information can be deduced from respective genotype/phenotype manipulations. Recently developed strategies to engineer C. acetobutylicum are summarized including the current portfolio of altered gene expression methodologies, as well as systematic (rational) and explorative (combinatorial) metabolic engineering approaches.