Nitrogen fixation refers to a chemical process in which molecular nitrogen, having a strong triple covalent bond, is converted into ammonia in the air or related nitrogenous compounds found in aquatic systems or soil. Atmospheric nitrogen is molecular dinitrogen that is generally a nonreactive molecule. Biological nitrogen fixation is a microbially mediated process, which utilizes the nitrogenase protein complex for transforming dinitrogen gas into ammonia. Sustainable agriculture refers to a type of farming which aims to fulfill the society's current requirements without compromising the capability of the future generations in meeting their needs. Nitrogen fixation is integral for sustainable food production and agricultural practices. This book provides comprehensive insights on biological nitrogen fixation and sustainable agriculture. Its aim is to present researches that have transformed the study of this subject and aided its advancement. The book is a resource guide for experts as well as students.