This book describes one approach to building and operating biogas systems. The biogas systems include raw material preparation, digesters, separate gas storage tanks, use of the gas to run engines, and the use of the sludge as fertilizer. Chapters included are: (1) "Introduction"; (2) "Biogas Systems are Small Factories"; (3) "The Raw Materials of Biogas Digestion"; (4) "The Daily Operation of a Biogas Factory"; (5) "The Once a Year Cleaning of the Digester"; (6) "Tanks and Pipes: Storing and Moving Biogas"; (7) "The Factory's Products: Biogas"; (8) "The Factory's Products: Biofertilizer"; (9) "The ABCs of Safety"; and (10) "Conclusion: Profiting from an Appropriate Technology." Many diagrams are provided throughout this handbook. New ideas, composting, bioinsecticides, ferrocement, facts and figures, sources and resources, feasibility studies, problem solving, and vocabulary are presented in the appendices. (YP)