(German: “braking radiation”), electromagnetic radiation produced by a sudden slowing down or deflection of charged particles (especially electrons) passing through matter in the vicinity of the strong electric fields of atomic nuclei. Bremsstrahlung, for example, accounts for continuous X-ray spectra—i.e., that component of X rays the energy of which covers a whole range from a maximum value downward through lower values. In generating bremsstrahlung, some electrons beamed at a metal target in an X-ray tube are brought to rest by one head-on collision with a nucleus and thereby have all their energy of motion converted at once into radiation of maximum energy. Other electrons from the same incident beam come to rest after being deflected many times by the positively charged nuclei. Each deflection gives rise to a pulse of electromagnetic energy, or photon, of less than maximum energy.

Bremsstrahlung is one of the processes by which cosmic rays dissipate some of their energy in the Earth's atmosphere. Solar X rays have been attributed to bremsstrahlung generated by fast electrons passing through the matter in the part of the Sun's atmosphere called the chromosphere.

Internal bremsstrahlung arises in the radioactive disintegration process of beta decay, which consists of the production and emission of electrons (or positrons, positive electrons) by unstable atomic nuclei or the capture by nuclei of one of their own orbiting electrons. These electrons, deflected in the vicinity of their own associated nuclei, emit internal bremsstrahlung.