Kernquadrupolresonanz / Phasenum wandlungen / ThermodynamikPrecision calorimetry can provide detailed information about the phase transitions in solids which is utilized to give insight into the nature of transitions and to check the model theories for their validity. Examples of studies are reviewed in this vein on the soft librational mode transition in p-chloranil, the orientational glass transition in carbon monoxide, and the order-disorder transition in hydrogen halides.