Gas-fermenting clostridia is a major class of chemoautotrophs that uses CO2 and CO to synthesize a variety of chemicals and fuels, thereby exhibiting good industrial application prospects. Wild-type gas-fermenting Clostridium species are inefficient in gas uptake, fixation and conversion and energy metabolism, and moreover, incompetent to produce high value products. In recent years, with the rapid development of omics, molecular genetic tools and biochemical techniques in gas-fermenting clostridia of which the physiology and metabolism as well as the underlying molecular mechanisms, metabolic design and engineering, and fermentation technologies have been widely studied. Here, we review the latest research progresses in gas-fermenting clostridia to provide information on these industrial microorganisms and bio-utilization of one-carbon gases.