Non-malignant, or "benign", diseases can be successfully treated using ionizing rad- tion technologies. It was first proposed in 1898 by Sokoloff, who reported the analgesic effects of radiotherapy for painful rheumatoid arthritis. Since then, the use of these techniques for painful muscle-skeletal diseases has gained acceptance particularly in Europe but is still carried out actively in the United States. Non-malignant diseases that are amenable to radiotherapy can be classified as inflammatory, degenerative, hype- roliferative, functional, or other disorders. However, the topographic and morphologic considerations are more relevant. Even though radiation therapy for "benign" diseases has not been pursued actively since the 1950s, more recent interest has dictated that it can be a very effective treatment modality. The use of radiotherapy can be justified for invasive and aggressive growth such as that seen with desmoids, for cosmetic d- figurations and functional loss as seen with keloids or endocrine orbitopathy, or for life-threatening complications such as hepatic hemangiomas or juvenile angiofibromas that occur in children or adolescents. Many of the non-malignant diseases can have a major and lasting effect on quality of life by causing pain or other serious symptoms, particularly when other methods of treatment are unavailable, have failed, or may induce more side effects. It is not generally the first choice of therapy in these non-malignant diseases, but it is acceptable as defined. The book edited by Seegenschmiedt et al.