I can't say enough good things about this book. If you are a leader, if you have a leader, if you hope to some day be a leader, if you are a parent, if you interact with human beings in any capacity, you need to read this book. Simon Sinek manages to explain the biology and psychology behind human interaction in an easy-to-understand way and make it funny at the same time. Have a highlighter and pen handy because you're going to want to take notes. I've found this book to be relevant to my job on a daily basis, and after reading it I have become more aware of my behavior and the behavior of others, and how the group dynamic is affected by it. I will be re-reading this book for the rest of my life.
If it wasn't the TED talk that brought you here, go check it out to watch a 45-min "cliff note" version of the book. And then come back and get the book anyway because it can't be thoroughly covered in 45 mins.