Methanogenesis occures in anaerobic conditions in vast natural and human made environments. The estimated 1% annual increase in global methane is mainly attributed to human activities. This article gives an overall perspective on methane-producing microbes, which are phylogenetically distinct from all other prokaryotes and eukaryotes, the food chain which produces atmospheric methane, and biochemical pathways leading to methane production in these microbes. 12 refs., 12 figs.