Ionising radiation can kill organisms that spoil food and can delay the sprouting or ripening of fruit and vegetables. Techniques for food irradiation first appeared more than 60 years ago in a patent appoiication for a method to kill parasites in meat with X-rays. However, it was only after 1945, when nuclear reactors could produce radioactive isotopes cheaply and efficiently, that anyone took food irradiation seriously. The physics of radiation as used on food is discussed. Benefits and dangers to carbohydrates, fats and proteins are discussed. (Abstractors note = Gamma radiation has been used in conservation, see ABSREM).