Soil Microbiology is a new branch of soil science. There are very few books dealing with practical aspects of soil microbiology. This book aims at presenting the methodologies of soil microbial activities which have direct and indirect effects on the growth and the yield of crops. The main objective in compilation of this manual is to highlight the beneficial soil microorganisms used as bio-fertilizers. The most significant of them are Azotobacter, Azospirillum, Pseudomonas, Bacillus, Rhizobium and VA mycorrhiza. This book contains assay of soil enzymes too. This book will be useful to students of biology, microbiology and agriculture.