With increasing population growth and the need for ever greater food production, it is becoming increasingly necessary to increase crop productivity combined with greater economy and sustainability of agricultural systems. Nitrogen fixation by the association between rhizobia and legumes meets these requirements. How to benefit from the process? By inoculating the seeds with the appropriate bacteria, called selected strains, the plant comes into contact with the microorganism to form the symbiosis. Symbiosis is the technical name of the intimate association that is formed between the bacteria and the plant. In Soil Microbiology, BNF is the area that has received the greatest research attention worldwide due to the fact that the practical application of the process is within reach of important cultivated legumes and the economic and environmental benefits and returns to society.