This paper describes the application of calorimetry to the measurement of the excess molar enthalpies H-m(E) for binary mixtures of nonelectrolytes. Batch, displacement, and flow calorimeters are described, using as examples the batch calorimeter of McGlashan;, the displacement calorimeters of Van Ness and of Marsh and Stokes, and the flow calorimeters of Christensen, Wormald, and Picker. Applications are described using calorimeters to measure H-m(E) for ((nonpolar + nonpolar), (polar + nonpolar), and (polar + polar)) mixtures. Excess enthalpies for liquid mixtures containing charge-transfer complexes and hydrogen bonds are used to help in understanding the nature of the molecular interactions in these systems. Applications involving measurements on liquid, gas, and supercritical fluid mixtures, including measurements in the near-critical region, are also described. The use of calorimetric measurements to determine {(liquid + liquid) and (vapor + liquid)} phase equilibria is discussed. Finally, equations used to represent H-m(E)(x) measurements are summarized.