Nitrogen fixation is widespread in the micro-organisms which live in soil, fresh water and tissues of higher plants and animals. in each of these environments, nitrogen-fixing organisms play their own specific roles. The principal need for a deeper understanding of biological dinitrogen fixation is the urgent requirement to increase agricultural production for an ever expanding human population in the developing countries. This review surveys the process of biological dinitrogen fixation in the soil with emphasis on practical utilization of nitrogen fixation in agriculture, since nitrogen assimilated by micro-organisms (biological dinitrogen) can replenish substantially the nitrogen reserves of the soil, help to improve soil fertility and thus make it possible to counteract the shortage of mineral nitrogenous fertilizers (through their judicious and more economical use). Briefly the biochemical and physiological pathways involved in biological dinitrogen fixation and recent advances in the genetics of biological dinitrogen fixation have also been reviewed. A need to establish a Rhizobium Research Centre in the country has been highlighted.