This book is an in-depth exploration of a variety of concepts that make up jazz improvisation. Hal jumps right right in with tons 'o examples about the elements that help you create your own great jazz lines. This book is not geared toward guitarists, but to musicians in general (Hal is a trombone player, and one of the most respected teachers at Berklee).
Beginners will not get much out of this book, but for the aspiring jazz player, this is a wealth of material for creating single-note lines and approaching soloing in general. It covers pacing, melody, guide-tone lines, dynamics, articulation, developing a motive, phrasing, all kinds of scales, and the use of triads. More importantly, it presents each concept with a practice regimen to help you learn and absorb it into your own playing.
Simply a must for anyone looking to get a grip on how to solo in the jazz genre and perhaps a bit more digestible than some other books of this type, like Mick Goodrick's Advancing Guitarist