Bradyrhizobium japonicum was described from soybean root-nodule bacterial isolates. Since its description, several studies have revealed heterogeneities among rhizobia assigned to this species. Strains assigned to B. japonicum group Ia have been isolated in several countries, and many of them are outstanding soybean symbionts used in inoculants worldwide, but they have also been isolated from other legume hosts. Here, we summarize published studies that indicate that group Ia strains are different from the B. japonicum type strain USDA 6T and closely related strains, and present new morphophysiological, genotypic and genomic evidence to support their reclassification into a novel species, for which the name Bradyrhizobium diazoefficiens sp. nov. is proposed. The type strain of the novel species is the well-studied strain USDA 110T (=IAM 13628T =CCRC 13528T =NRRL B-4361T =NRRL B-4450T =TAL 102T =BCRC 13528T =JCM 10833T =TISTR 339T =SEMIA 5032T =3I1B110T =ACCC 15034T =CCT 4249T = NBRC 14792T =R-12974T =CNPSo 46T). © 2013 IUMS.