In this comprehensive volume leading international researchers review in depth virtually every aspect of this important subject, including the nitrogen cycle, nitrogenase enzymes, the nif genes, oceanic nitrogen fixation, host-microbe interactions, root nodule metabolism, model legume systems, mycorrhizal interactions, genomics of diazotrophs, symbiotic islands in Mesorhizobium, bacterial endophytic associations, and much more. The book emphasizes the importance of nitrogen fixation as a model for the analysis of many other biological processes and will be useful to a wide range of scientists. Significantly, the authors have succeeded in conveying the sense of fun and excitement experienced by those involved in this important area. This comprehensive volume will serve as a valuable reference work for all scientists working in this field and will also be of interest to researchers studying metal-containing enzymes, symbioses, genome research, environmental microbiology, plant metabolism, infection events and other prokaryote-eukaryote interactions.