1995 marks the centennial year of the discovery of x-rays. The medical profession advanced rapidly following Roentgen's discovery of the x-ray. Every aspect of medicine came to rely on radiology in some way. The x-ray not only revolutionized diagnostic medicine, it transformed therapeutic medicine as well. Only months after its discovery, the x-ray was being used with therapeutic intent, thus began radiation therapy. We can examine the development of radiation oncology in several periods.