Butanol has been used as an important solvent in various industries, and is considered a good liquid fuel substitute for gasoline for use in internal combustion engines. Biobased production of butanol has a long history and was one of the first industrial-scale fermentation processes in which Clostridium strains were employed. Recent work on metabolic engineering of Clostridium strains has resulted in considerably improved production of butanol. In addition, several non-clostridial microorganisms have also been developed for butanol production. Here we review the advances in butanol production that have employed Clostridium strains and other microorganism