Anaerobic digestion is a major field for the treatment of waste and wastewater. Lately the focus has been on the quality of the effluent setting new demands for pathogen removal and for successful removal of unwanted chemicals during the anaerobic process. The two volumes on Biomethanation are devoted to presenting the state of art within the science and application of anaerobic digestion. They describe the basic microbiolgical knowledge of importance for understanding the processes of anaerobic bioreactors along with the newest molecular techniques for examining these systems. In addition, the applications for treatment of waste and wastewaters are presented along with the latest knowledge on process control and regulation of anaerobic bioprocesses. Together these two volumes give an overview of a growing area, which previously has never been presented in such a comprehensive way.