An analysis is presented of possible worldwide production of methane from anaerobic decay of organic municipal and industrial wastes in landfills. The amount of methane released to the atmosphere from this source may now be in the range of 30–70×106 T/yr, which is between 6% and 18% of the total CH4 source. By far, most of this emission comes from the industrialized world. Release rates from these countries have been increasing steadily during the past decades, but growth rates are now gradually stagnating. In the future, the contribution from developing nations is expected to grow rapidly because of increasing population and urbanization. Consequently, methane release from landfills may become one of the main sources of atmospheric methane in the next century.