I wish there were more books like this. It takes an author who has written a great deal (Ken Wilber in this case) and asks for serious critiques from others who have written in the same field. It then gives the author a chance to reply, and the other to respond to his replies. The final chapter is jointly written by the author and the editors. For anyone who is interested in the question - "How is Wilber rated by others in the field?" - this is essential reading, and very well done.