Rhizobium tropici is a fascinating, but still little studied, rhizobial species originally isolated from root nodules on common bean and species of Leucaena in South America; the species has also been found in soils of other continents, establishing symbioses with several legume hosts. Currently, R. tropici encompass a variety of strains, some now reclassified in genetically related species, with an emphasis on R. leucaenae and R. freirei. Interest in the evolution of the “R. tropici group” rises from its close genetic resemblance with agrobacteria, indicating the interesting possibility of discovering a linkage between symbiosis and pathogenicity. Two strains, R. tropici CIAT 899T and R. freirei PRF 81T are of particular interest: due to their high capacity of nitrogen fixation, they are broadly used in commercial inoculants. Both strains have been subject of several genomic and proteomic studies. Genome sequencing has shown that CIAT 899 and PRF 81, in addition to R. leucaenae CFN 299T, share almost identical symbiotic plasmids, with interesting features as two nodA and five nodD genes. “R. tropic group” strains have also an outstanding tolerance to environmental stresses, and several genes related to this feature were described in the genome and confirmed in proteomic studies under high temperature and acidic conditions. A very fast transcription of genes related to nodulation and to the biosynthesis of polysaccharides was also verified in the presence of common-bean-seed exudates. Altogether, the features emphasize the importance of “R. tropici group” for evolutionary studies, and the potential of several strains as biotechnological resources.