I read this book a couple of years ago.
As negotiation is part of my role it was very helpful to me in my work. The book is easy to read and could be summarized on one page (which I did).
Earlier in the year I attended a two day workshop on negotiation and required reading was the same book. I discovered at the workshop that I had only scratched the surface on negotiation and I have worked a bit harder on it since. The point was made at the workshop, and very correctly, that negotiation is something we do at work and at home, all the time in fact. Doing it consciously and from a non-positional stance is very productive, being prepared is essential and being mindful during the negotiation is helpful!
If you want to know more - read the book.