Biofertilizer has been proven successful technology in many developed countries. The use of Biofertilizer improves soil fertility by fixing atmospheric nitrogen, solubilizing insoluble phosphates, producing plant growth-promoting substances in the soil and promoting nodulation ability, which increases the yield by 20-80%. The term biofertilizer or microbial inoculants/fertilizer is defined as a preparation containing live or latent cells of efficient strains capable of nitrogen fixation, phosphate solubilization which are used for application of seed, soil with the objective of increasing the numbers of such microorganisms and accelerate certain microbial process to enhance the degree of the availability of nutrients to plants [1]. Increasing cost of chemical fertilizers is unaffordable by small and marginal farmers. There is found depletion of soil fertility due to widening gap between nutrient removal and supplies. By considering the threat to sustainable agriculture by the use of chemical fertilizers and human activity there is growing concern about environmental hazard management. In developing countries exploitation of bio- inoculants is hampered by several factors [13]. Long term use of organic fertilizers is economical, eco-friendly, more efficient, productive and accessible to marginal and small farmers over chemical fertilizers. The chapter provide overview knowledge about different bacterial, fungal and algal biofertilizer, its association with plants and transformations of nutrients in soil.