This collection investigates the nature of improvisation as the defining element of jazz through the profiles of sixteen influential musicians. Whitney Balliett, a long-time contributor to The New Yorker, utilizes his extensive experience as a jazz critic to document the lives and creative processes of artists across the history of the genre. By observing these musicians in unguarded moments, the author constructs a framework that connects personal temperament to the spontaneous act of musical creation.

Critics frequently cite Balliett as a master of the journalistic profile, noting his ability to capture the specific cadence of a musician's personality. Experts consider this work a foundational text for understanding the intersection of jazz history and the individual artist's creative process.