Radiotherapy, also called radiation therapy, is the treatment of diseases using ionizing radiation. Ionizing radiation is used for both therapeutic and diagnostic purposes. For therapy high-energy radiation in megavoltage range is preferred whereas for diagnosis kilovoltage energy is used. Radiotherapy is one the important options in the treatment of oral cancer. A dental surgeon needs to know the basics of radiation therapy because he forms a vital part of the team of health care professionals involved in managing this dreaded scrouge on humanity. His role in diagnosis, treatment and follow-up of radiotherapy patients is highlighted in this discussion.