In calorimetry, the heat-flow to or from a sample is measured as a function of time (isothermal calorimetry) or temperature (scanning calorimetry). The technique is not dependent on the physical form of the sample and is usually non-destructive (exceptions include temperature-induced irreversible phase transitions and thermal decomposition). The inherent sensitivity of modem instruments allows measurements on the micro-Watt scale. Calorimetry is highly suited to the study of pharmaceutical systems because small sample masses are usually required and the technique is very sensitive to changes induced by, for instance, formulation or processing. It is the purpose of this review to show applications of both isothermal and scanning calorimetry in the field of physical and bio-physical pharmacy. Potential applications include studies of physical stability, excipient compatibility, chemical stability and the study of the potential interactions of and between macromolecules such as lipids, surfactants, and nucleic acids,