Methane oxidation can occur in both aerobic and anaerobic environments; however, these are completely different processes involving different groups of prokaryotes. Aerobic methane oxidation is carried out by aerobic methanotrophs, and anaerobic methane oxidizers, discovered recently, thrive under anaerobic conditions and use sulfate or nitrate as electron donors for methane oxidation. This review will focus on the aerobic oxidation of methane.