An infant born in the US today will probably live more than twenty years longer than the average lifespan a century ago. While living well into the eighties and nineties is becoming more and more attainable, how many more years can humanity expect to gain? And how can we raise the quality of those later years? The two main barriers are accumulated damage to cells and organs that occurs over time and age-related illnesses like cancer and Alzheimer's disease. Researchers are divided over where to pour their efforts, and in The Science of Aging, we take a look at what science knows--and what it's striving to learn--about the aging process.