This chapter discusses radiotherapy in head and neck cancers, where radiotherapy is a treatment with electromagnetic radiations, X-ray or gamma rays and particles which produce ionisation in the body. Gamma rays are emitted from radioactive isotopes which exist in natural and artificial forms. Radiations in megavoltage range have a very high penetrating power and better percentage depth dose. The value of radiation or indeed the whole basis of radiotherapy rests on its capacity to destroy malignant growth in situ without producing destruction of normal tissues in which tumour is growing and which necessarily receives an equal amount of radiations. Palliative radiotherapy is used in very advanced cases which have distant metastasis, general condition is too poor due to heart, lung or kidney diseases, in bleeding, pain or obstruction to air or food channels. Xerostomia is the most common long-term side effect of radiotherapy. Important side effects of radiotherapy are skin reaction, dryness, local oedema, mucosal reactions and malignancy.