AbstractThe diversity of nitrogen-fixing Leguminosae [Fabaceae]-nodulating bacteria (LNB) in Brazil and the efficiency and application of LNB isolates are discussed. The relationships between NB strains and Leguminosae species are divided into three main groups: non-symbiotic; symbiotic non-efficient; and symbiotic efficient. The current taxonomy of LNB and the evolution of the symbiosis as well as the phenotypic and genotypic approaches to taxonomic and diversity studies are also covered. The factors affecting LNB populations are evaluation methods, agronomic practices (e.g., tillage and crop rotation), soil pH, liming and antibiotic tolerance, nutrients, and mining.