Since the discovery of radium and with the progressive availability of newer sources of ionizing radiation, radiotherapy has become an integral part of the treatment of cancers of the oral cavity and oropharynx. Radiation may be employed as a single modality or in combination with chemotherapy, either as a definitive treatment or as an adjuvant treatment following surgery. The goal of radiotherapy is to achieve maximal cell death with minimum tissue damage to normal structures and hence minimal acute toxicity and long-term sequelae.