Irradiation is the process by which an item is exposed to radiation. In common usage the term refers specifically to ionizing radiation, and to a level of radiation that will be destructive to life, rather than simply exposure to normal levels of radiation, or background radiation.

Most forms of radiation do not induce a state of radioactivity in objects. An example of this is gamma rays. Gamma rays are very-short-wavelength electromagnetic radiation, and are extremely energetic and deleterious to life. If administered at appropriate levels, they can be used to sterilize objects, a technique used in the production of medical instruments and disposables, such as syringes as well as in the disinfestation and sterilization of food. Gamma rays can also have a preservative effect by killing raw foods, i.e. preventing grain and potatoes from sprouting.

Food irradiation is a potentially important method of food preservation that is the subject of significant controversy, arguments coming back to life after the idea of irradiating food had been discarded in the sixties.

During the 2001 anthrax attacks, the US Postal Service irradiated mail, damaging it in a few cases.

See also: Radiolyse