This study is conducted to investigate heat and gas production at a municipal solid waste landfill. Periodic temperature and gas measurements have been taken at approximately 140 locations within the waste mass, liner systems, and cover systems at a midwestern U.S.A. landfill since 1999. Increasing temperatures (1 to 15°C/a) were observed for newly placed wastes whereas steady elevated temperatures (50 to 60°C) were observed in older wastes. Liner temperatures increased at a rate of approximately 2 to 4°C/a and stable elevated temperatures in excess of 30°C were observed after 5.5 years and under 42 m of waste height. Anaerobic decomposition and steady landfill gas production commenced within weeks or months of waste placement. Variability of both temperatures and gas levels was observed in wastes due to seasonal climatic fluctuations at shallow depths, whereas relatively stable measurements were obtained at greater depths. The majority of temperature increases for wastes and liners occurs under anaerobic conditions.