This study was conducted to investigate thermal aspects of municipal solid waste landfills as a function of operational conditions and climatic region. Spatial and temporal distributions of waste temperatures were determined at four landfills located in North America (Michigan, New Mexico, Alaska, and British Columbia). Temperatures of wastes at shallow depths (extending to 6 to 8 m depth) and near the edges of a cell (within approximately 20 m) conformed to seasonal temperature variations, whereas steady elevated temperatures (23 to 57°C) with respect to air and ground temperatures were reached at depth and at central locations. Waste temperatures decreased from the elevated levels near the base of landfills, yet remained higher than ground temperatures. Thermal gradients in the range of approximately -30 to +22°C/m with average absolute values typically less than 5°C/ m were measured within the wastes. Heat content (HC) of wastes was determined as the difference between measured waste mass temperatures and unheated baseline waste temperatures at equivalent depths. Peak HC values ranged from 12.5 to 47.8°C day/day. The peak HCs were directly correlated with waste placement rates and initial waste temperatures, and they occurred at a specific average precipitation (2.3 mm/day) beyond which further precipitation did not contribute to heat generation. HC was determined to conform to exponential growth and decay curve relationships as a function of climatic and operational conditions. Heat generation was determined based on HC using ID heat transfer analysis. The heat generation values ranged from 23 to 77 MJ/mwithout losses and were significantly higher than biochemical prediction models, yet lower than values from incineration analyses. Overall, the highest values for temperatures, gradients, HC, and heat generation were observed in Michigan, followed by British Columbia, Alaska, and New Mexico. Integrated analysis of temperature and gas composition data indicated that temperature increases and HC values were greater during anaerobic decomposition than aerobic decomposition. Sustained high temperatures and heat generation occurred in wastes under anaerobic conditions. Journal of Geotechnical and Geoenvironmental Engineering © ASCE.