Calorimeters were originally developed as instruments that measure energy deposits through changes in temperature. In nuclear and particle physics, this class of instruments is used to measure the properties of particles carrying energies ranging from a small fraction of 1 eV to 1020eV or more. And these properties are not limited to the energy carried by these particles, but concern the entire four-vector, including the particle mass and type. In many modern experiments, large calorimeter systems play a central role. In this chapter, we review this role, and the important calorimeter properties deriving from it. We also give an overview of the most common types of calorimeters, classified according to the type of particles and the energy range for which they are intended.