Average human life expectancy at birth in the United States has increased dramatically in the past one hundred years, from 49 at the turn of the twen- tieth century to 77 for men and 81 for women (and it’s slightly higher in Canada and Japan).6 But this remarkable increase has not been accompanied by an equivalent increase in health span. Most of us would rather extend our health span than our life span. This rational desire has motivated a significant amount of recent research into the biology of aging. In this book, I will focus on many of the exciting recent results in this field, which suggest some easy (and some not-so-easy) ways to live healthier while living longer.