The atmosphere provides most of the oxygen, carbon, and nitrogen that we depend on, but until now has been thought to lack sufficient energy to sustain life. Here I will demonstrate that diverse microbes live by harvesting the low concentrations of hydrogen and carbon monoxide from air using high-affinity hydrogenases and carbon monoxide dehydrogenases. Through research focused on the model bacterium Mycobacterium smegmatis, I will summarise how we determined the enzymatic mediators, physiological role, and structural basis of this process. I will then discuss how we have applied these insights to achieve cell-free air-driven ATP synthesis and make the first air-powered fuel cells. These findings redefine the minimal requirements for life and reveal new ways that microbes regulate our atmosphere.