Synopsis Soil factors such as organic matter content, soil structure, nutrient content, nutrient cycling, nutrient availability, and water holding capacity are all influenced by, or dependent upon, soil microorganisms. A fascinating and relatively new area of soil microbiology is the study of how these microscopic life forms communicate and interact. This book is being prepared by keeping in view the syllabi of several universities. Arrangement of chapters and topics is as such that it is easily followed by the students. The text matter is clear and simple, which is explained through various diagrams. It is hoped that the publication is useful not only to the students but also to academic professionals.