"For something that all humans do for hours every night, sleep is not that well understood. One thing we do know, though, is that sleep is crucial for our health and happiness. Here's a highly readable and fascinating look at why sleep is so important, what's happening in our bodies while we're sleeping (it's a lot more than you think!), and how the science of sleep research has evolved. It probes some of the mysteries about sleep, like why we need sleep, why we dream, and even how long we can go without sleep! It also explains why teens and tweens aren't getting enough sleep -- and what school principals can do about it!."