When two proteins interact and bind, conformational changes in the proteins, and rearrangement of the solvent in the vicinity of the binding site, result in the absorption or generation of heat. Quantification of this reaction heat by ITC provides a complete thermodynamic description of the binding interaction, the stoichiometry of binding, and the association constant; in addition, if structural information is available, the contributions of specific amino acids mediating the binding event can be identified and their thermodynamic contributions quantified.