A review is presented of calorimetric measurements of the heats of combustion and other reactions. The precision of the measurements is discussed, and possible sources of error in combustion calorimetry are considered. Measurement of the heats of formation of the oxides and other compounds is also discussed. Recent developments in calorimetry are described briefly, including the rotating bomb calorimeter, use of gases other than oxygen, fluorine bomb calorimetry, and combustion bomb with window. Tables are presented of the heats of reactions measured by oxygen bomb calorimetry, nitrogen bomb calorimetry, and fluorine bomb calorimetry. (D.L.C.)