While I may be a bit biased towards the fretless bass - this book is certainly very well done. Chris Jisi, from Bass Player, has assembled some of the most influential fretless players on the planet, to talk about technique, music, style, and technical aspects of fretless bass. The book is well organized, with some great information about music available, as well as who's playing what.
The book is rounded out by some great luthiers and builders discussing care & feeding of a proper fretless.
I also love the center section with some full page, and full color, Bass Player Magazine covers of great fretless players that have graced their pages. That's a very nice bonus.
If you are at all interested in fretless bass - this book is a keeper!
Wes Watson
FretlessBassist.com