Many plants enter a beneficial symbiosis with soil bacteria broadly called 'rhizobia'. The legume family, including peas, beans, soybeans, peanuts, clovers and alfalfa, is most significant as it produced critical foods as well as animal feeds and biofuels. The symbiosis results in the novel development of new plant organs on the roots of legumes; inside these, the invading bacteria are housed and convert to nitrogen fixing bacteroids. As much as 400 kg of nitrogen is made available per year, adding to the benefit by reducing fertiliser-based nitrogen supply leading to water pollution and N₂O greenhouse gas release. The last two decades have seen huge scientific advances in our understanding of the key mechanisms involved in this symbiosis. Genetics, genomics and biochemistry have clarified the bacterial components leading to nitrogen capture. Plant genes controlling the formation of the root nodules and the invasion of the bacterium have been isolated and characterised. An universal legume process called Autoregulation of Nodulation (AON) was mechanistically investigated leading to the recognition that bacterial infection induces specific plant peptides. These travel to the leaf where they are recognised by a specific receptor kinase, which leads to the eventual inhibition of continued nodulation by molecular mechanisms involving microRNA, transcriptional factor regulation and novel nodulation control genes. These advances from molecular biology, genomics, microbiology and genetics are hoped to improve the utility of legumes in modern agriculture, increasing food output and decreasing the environmental footprint.