While we’ve all heard the old joke that physics saves lives because its introductory courses keep sub-par students out of medical school, physicists have, both historically and presently, contributed immensely to the advancement of medicine. This talk will survey the myriad roles physicists play in the medical field, with a special focus on a medical physicist’s responsibilities in the treatment of cancer with ionizing radiation. Medical physicists who specialize in radiation oncology are vital to assuring the safe and accurate delivery of therapeutic radiation to cancer patients. The clinical practice of radiation therapy will be reviewed, including the current state of the art in radiation delivery as well as physicists’ contributions to both the application of existing therapies and the development of new technologies. Finally, I will discuss the training/certification requirements for clinical physicists and why the field would benefit greatly from more Mudd grads pursuing careers in medical physics.