This book Azotobacter in Sustainable Agriculture is designed to meet the needs of researchers and scholars working on Azotobacter in particular and diazotrophs in general.The fourteen chapters included in this book encompassing wide range of topics are contributed by well- – known research workers. For systematic and comprehensive reading the chapters have been resolved into five different sections ranging from genetic and ecological aspects physiology and metabolism microbe-microbe and microbe-plant interactions and finally role of Azotobacter as a biofertilizer in sustainable crop production. Hope this book will provide much needed fillip.