The measurement of the energetics of biological processes such as biochemical reactions, association of ligands to biological macromolecules, folding of proteins into their native conformations, phase transitions in biomembranes, and enzymatic reactions, among others. Two types of instruments have been developed to study these processes: differential scanning calorimeters and isothermal titration calorimeters. Differential scanning calorimeters measure the heat capacity at constant pressure of a sample as a continuous function of temperature. Isothermal titration calorimeters measure directly the energetics (through heat effects) associated with biochemical reactions or processes occurring at constant temperatures. In all cases, the uniqueness of calorimetry resides in its capability to measure directly and in a model-independent fashion the heat energy associated with a process.