Methane oxidation has been measured in several acidic environments, including peatlands, forest soils, and terrestrial geothermal features. Aerobic methanotrophic bacteria have been detected in each of these environments using molecular cultivation-independent methods, and anaerobic methanotrophs are also suspected to be active in peat. Most known methanotrophs are neutrophilic, but moderately acidophilic alphaproteobacterial methanotrophs have been isolated and characterized. These grow between pH 4.2 and 7.5, and appear to be the predominant methane-oxidizing species in acidic peatlands and forest soils. Extremely acidophilic methanotrophs able to grow below pH 1 and belonging to the phylum Verrucomicrobia have also been isolated from geothermal habitats. This chapter outlines the ecology, physiology, taxonomy, and genetics of methanotrophs in acidic environments.