The science of plant-microbes interaction (PMI) plays a major role in agriculture especially in the field of crop production and protection by beneficial plant growth promotion microorganism (PGPM). This book is the study of PGPM and the fundamental aspects of microorganisms and their direct and indirect relationship to agriculture and plant growth promotion. The book begins with some basic information on Plant-microbial associations that help in growth promotion and protection including methods of study and classification. It then goes on to describe their utilization and effects in agriculture as growth promoters and biofertilizers. This book deals with the various aspects of soil nutrient management and agricultural microbiology. Special attention is given to the plant growth-promoting micro-organisms in the soil, their interactions, and roles. A major discussion on soil AMF and its effect on plants and bioinformatics tools-application in PMI are also given. Thus in a broad sense, the book will be useful to the students and researchers of Agricultural Microbiology. Globally we need to improve the production and protection of crops through modern biotechnological techniques.