The theme of this volume, "Medical Applications of Accelerators", is of enormous importance to human health and has a deep impact on our society.The invention of particle accelerators in the early 20th century created a whole new world for producing energetic X-rays, electrons, protons, neutrons and other particle beams. Immediately these beams found revolutionary applications in medicine. There are two important yet distinct medical applications. One is that accelerators produce radioisotopes for various nuclear medicines for millions of patients each year. The other is that accelerators produce particle beams for radiation therapy for the treatment of cancer. The particle beams can be X-rays (generated by high-energy electrons), protons, neutrons or heavy ions such as carbon. Today there are more than 5,000 accelerators routinely used in hospitals all over the world for nuclear medicine and cancer therapy. The great potential of accelerator applications in medicine can hardly be exaggerated.This volume contains 14 articles, all written by distinguished scholars.