Spectrometers are devices for the precise measurement of energies or masses of the particles in a beam. These devices are used, for example, in the secondary beams to sort out the products of high-energy or nuclear reactions. Charged particles produced in these reactions are guided through a spectrometer to analyzing stations. Although no acceleration is performed on these particles, accelerator physics is needed to manipulate them. The working principle is similar to that of the prisms in light optics. In order to be able to detect rare events, of particular concern are issues of high resolution, large angular, and energy acceptance, and being able to handle a wide variety of beams and targets. For short-lived products, it is also necessary to make the spectrometer path as short as possible.