“Zero Hunger” is one of the several Sustainable Development Goal can be achieved by an ever-green revolution. The nitrogen-fixing bacteria are game-changer and prime players for nitrogen homeostasis in the ecosystem. The playbacks of biological nitrogen fixation in the agroecosystem have been realized from symbiosis to associative and free-living interaction in a broad range of non-legume crops. The jab of various rhizobia, non-rhizobia, and free-living bacteria to the non-legumes has commenced, where they set themselves intercellularly within the root system, fixing nitrogen for enhanced crop production. This book marks new frontiers of Nitrogen-Fixing Bacteria and their versatile interaction with Non-legume and Sustainable Growth.