Since the general recognition of the Archaebacteria, research into the evolution, metabolism, molecular biology and ecological roles of these fastidious anaerobes has proceeded at an ever-increasing pace. All possess a very novel biochemistry and many exploit unique ecological niches. Methanogens, which convert one-and-two carbon compounds into the important atmospheric gas methane, are the largest group among the Archaebacteria. Of all microbial groups, methanogens provide perhaps the best opportunity to study evolution because of their phyologenetic diversity and unique biochemistry. Today, the analysis of methanogens is at a threshold. Molecular-biological studies of these microorganisms are revealing more and more processes unique to this group, and in turn, studies of methanogens are providing new perspectives to the broader fields of biochemistry and molecular biology. This volume is the first book to be published on methanogenesis, and it will provide the reader with a comprehensive view of the field and point to future trends.