Aging—not cancer, not heart disease—is the underlying cause of most human death and suffering. The same cascade of biological changes that renders us wrinkled and gray also opens the door to dementia and disease. We work furiously to conquer each individual disease, but we never think to ask: Is aging itself necessary? Nature tells us it is not: there are tortoises and salamanders who are spry into old age and whose risk of dying is the same no matter how old they are, a phenomenon known as “biological immortality.” In Ageless, Andrew Steelecharts the astounding progress science has made in recent years to secure the same for humans: to help us become old without getting frail, to live longer without ill health or disease.