Walker taught me a lot about this basic activity that every person on Earth needs. I suspect his book will do the same for you." --Bill Gates A New York Times bestseller and international sensation, this "stimulating and important book" (Financial Times) is a fascinating dive into the purpose and power of slumber. Sleep is one of the most important but least understood aspects of our life, wellness, and longevity. Compared to the other basic drives in life--eating, drinking, and reproducing--the purpose of sleep remained elusive. An explosion of scientific discoveries in the last twenty years has shed new light on this fundamental aspect of our lives.