Advances in the design and operation of particle accelerators built for basic physics research are leading to the rapid evolution of machines that deliver cancer-killing beams. The trend has been toward less expensive, more versatile particle beam delivery systems, designed for improved efficacy and greater access for cancer patients around the world. Because proton and ion beams deposit most of their energy where the beam stops rather than as they travel through tissue, they can deliver cell-killing energy with extreme precision, allowing lower dosing with less damage to adjacent healthy tissue than conventional X-ray or electron radiation treatments. This symposium explores the scientific rationale behind hadron beam therapy from the perspectives of a physicist who designs state-of-the-art particle accelerators, a radiobiologist exploring how those particle beams affect cells and tumors, and an oncologist. It also addresses the question of relative efficacy of hadron therapy compared to conventional radiation treatment, as well as the challenges of leveraging scientific expertise to bring advances driven by basic research to the benefit of society at large.