Autotrophic acetogenic bacteria are able to capture carbon (CO or CO2) through gas fermentation, allowing them to grow on a spectrum of waste gases from industry (e.g., steel manufacture and oil refining, coal, and natural gas) and to produce ethanol. They can also consume syn(thesis) gas (CO and H2) made from the gasification of renewable/sustainable resources, such as biomass and domestic/agricultural waste. Acetogenic gas fermentation can, therefore, produce ethanol in any geographic region without competing for food or land. The commercialization of the process is now at an advanced stage. The real potential of acetogens, however, resides in their capacity to produce chemicals and fuels other than ethanol. This requires the redesign and implementation of more efficient metabolic pathways, adapting them to high performing manufacturing processes. Respective species, their bioenergetics, the genetic tools developed for their metabolic engineering, culture techniques and fermenter set-ups, as well as the commercialization, are comprehensively described and discussed in this chapter.