In dual-energy CT (DECT), two CT datasets are acquired with different x-ray spectra. These spectra are generated using different tube potentials, partially also with additional filtration at 140 kVp. Spectral information can also be resolved by layer detectors or quantum-counting detectors. Several technical approaches-that is, sequential acquisition, rapid voltage switching, dual-source CT (DSCT), layer detector, quantum-counting detector-offer different spectral contrast and dose efficiency. Various postprocessing algorithms readily provide clinically relevant spectral information.DECT offers the possibility to exploit spectral information for diagnostic purposes. There are different technical approaches, all of which have inherent advantages and disadvantages, especially regarding spectral contrast and dose efficiency. There are numerous clinical applications of DECT that are easily accessible with specific postprocessing algorithms.