Like other leguminous plants, the Lima bean (Phaseolus lunatus) establishes a mutualistic symbiosis with nitrogen-fixing bacteria commonly known as rhizobia. These bacteria elicit the formation of nodule structures on the roots where they become intracellular and fix atmospheric nitrogen for the plant. The Lima bean shows apreference to form nodules with slow-growing bacteria of the genus Bradyrhizobium unlike its congeneric species, the common bean (Phaseolus vulgaris), which prefer fast-growing rhizobial strains. P. lunatus was independently domesticated in the Andes and Mesoamerica by pre Columbian societies Knowledge of the genetic biodiversity of Lima bean symbionts has increased in recent years with data obtained in its domestication areas. In Peru,Lima beans host Bradyrhizobium yuanmingense, Bradyrhizobium paxllaeri, Bradyrhizobium icense, and a yet unnamed genospecies. At least seven Bradyrhizobium genospecies have been found in P. lunatus nodules in Mexico. Thisrhizobial richness indicates a relative promiscuity of Lima bean in contrast to previous statements that this plant was a restricted host for nodulation. Interestingly, Mexican and Peruvian bradyrhizobia are distinct, perhaps in relation to the different plant gene pools from which domestication occurred in those geographic areas. Besides Bradyrhizobium, other rhizobial genera such as Rhizobium, Sinorhizobium and Mesorhizobium can be found in Lima bean nodules in its domestication centers and in other areas. Although effective nodulation with these genera has been reported, the ecological relevance of those associations is presently unknown.