This book is an attempt to compile information from scientists and academia working in the field of AIMs. The book encompasses different Agriculturally Important microorganism (AIMs), mechanism of action and mode of application for sustainable agriculture. The potential of microbes in nitrogen fixation, solubilizing nutrients like phosphorous, Potassium, tolerance to etc. are the major strength of the book. There is relatively a new frontier, use of Plant Growth Promoting Rhizobacteria (PGPR)in enhancing crop productivity. These microbes inhabit at the rhizospheric region of the root and facilitate plant growth through a variety of direct and indirect mechanisms.These PGP have been identified to solubilize phosphate, Potassium, Zinc, produce siderophore, IAA, Hydrogencyanide, fix ammonia and many more. Today, such microbes are extensively studied not only as a biofertilizer or fortification of nutrient to the plant, but also a potential agent to decrease application of chemical fertilizer and other agrochemicals. The book also gives an insight to this aspect also. Last but not the least, a light has been thrown on use and application of nano-biofertilizer for sustainable agriculture.