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 6(T) 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 110(T) (=IAM 13628(T) =CCRC 13528(T) =NRRL B-4361(T) =NRRL B-4450(T) =TAL 102(T) =BCRC 13528(T) =JCM 10833(T) =TISTR 339(T) =SEMIA 5032(T) =3I1B110(T) =ACCC 15034(T) =CCT 4249(T) = NBRC 14792(T) = R-12974(T) = CNPSo 46(T)).