 Nitrogenases are enzymes that convert nitrogen gas, N2, into ammonium, and H4+, which can then be used by plants as a source of nitrogen. Synthetic biology has been used to engineer these enzymes into plants and bacteria to reduce their reliance on industrial nitrogen fertilizers. Recent research is focused on improving the activity and oxygen tolerance of nitrogenases, as well as engineering them into symbiotic relationships with plants. This article was authored by Emily M. Bennett, James W. Murray, and Mark Iceland.