Bradyrhizobia form a genetic phylum of which some strains have the ability to fix nitrogen symbiotically with legumes. A recent study shows that they are the most ubiquitous and abundant bacteria in soils. They are also used to inoculate the main legume crops (soybean, peanut, cowpea, etc.) making these bacteria probably the most exploited by man. During this presentation, I will present different reasons that could explain such an ecological success. In particular, their very large genome, nearly 10 Mb, which codes for a myriad of transporters, sensors, regulators, enzymes and other functions... constitutes a key that could explain their adaptation to highly variable environmental conditions. Their outer membrane which presents a unique LPS structure with associated cholesterol analogues (hopanoids), which reinforce the cohesion between the 2 membrane layers, is a major asset improving their resistance to various biotic and abiotic stresses. Finally, these bacteria are able to associate symbiotically with a very large diversity of legumes thanks to the use of different strategies, involving or not, Nod factors signal, and in some cases the type III secretion system. All these properties make these bacteria a very important genus to consider for improving plant health and environment.