Methane is a potentially inexpensive, widely available electron donor for biological denitrification of wastewater, landfill leachate or drinking water. Although no known methanotroph is able to denitrify, various consortia of microorganisms using methane as the sole carbon source carry out denitrification both aerobically and anaerobically. Aerobic methane-oxidation coupled to denitrification (AME-D) is accomplished by aerobic methanotrophs oxidizing methane and releasing soluble organics that are used by coexisting denitrifiers as electron donors for denitrification. This process has been observed in several laboratory studies. Anaerobic methane oxidation coupled to denitrification (ANME-D) was recently discovered and was found to be mediated by an association of an archaeon and bacteria. Methane oxidizing consortia of microorganisms have also been studied for simultaneous nitrification and denitrification (SND) of wastewater. This review focuses on the AME-D process, but also encompasses methane oxidation coupled to SND as well as ANME-D.