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Synopsis Micro-organisms are important for all forms of agricultural and or her natural eco-systems. Microbial processes operate and are vital but are not manipulated or controlled to any great extent, particularly in the field of agriculture. Indeed an understanding of many of them is still extremely limited. The present volume is an attempt to bring under one roof an account of different groups of micro-organisms that play an important role in integrated nutrient supply systems and agricultural eco-systems. They not only provide plant nutrients but also maintain the health of the soil. The chapters are written by scientists known for their commitment to particular group of organisms and have worked in and have considerable experience of agricultural production processes. The role of biological nitrogen fixation in plant nutrition, principally involving legumes is well substantiated and documented. The potential and prospects of Rhizobium bio-fertilizers are examined in detail by Dr. A.K. Saxena and Dr. S. Kannaian. The chapter also deals with inoculation of Rhizobium/Azo-rhizobium in Sesbania species. The basic aspects such as signal molecules in legume-Rhizobium symbiosis is discussed by Dr. G.P. Brahmaprakash and Dr. D.S. Bagyaraj and Rhizobium-legume interaction is dealt with by Dr. K.K. Rao. We now have a greater awareness of the associative symbiosis such as Azospirillium, the current status of which is examined in detail in the chapter by Drs. Geeta Singh and K.V.B.R. Tilak. The mycorrhizae have long held a respectable position in agricultural and forest eco-systems. Our knowledge and understanding of the biology of these organisms, though severely hampered by our inability to culture them axenically in the laboratory has increased greatly in the last two decades, not least through the major contributions by Dr. D.S. Bagyaraj, who along with his colleague Dr. V. S. Mehrotra discusses systematics, taxonomy and phylogeny of arbusculer mycorrhizae. It is one's experience that in the agricultural fraternity the role of mycorrhiza fungi and their benefits to the plant is poorly understood and often overstated. We are indeed fortunate that we have an account by Dr. K.G. Mukherjee along with Dr. P. Mago, of the mycorrhizal technology in forestry and agriculture. There has been considerably emphasis on phosphate solubilization by micro-organisms to release the bound phosphorus and make it available to the crop plants. Dr. A.C. Gaur discusses phosphate solubilizing micro-organisms.