Boulez is one of the most controversial and enigmatic personalities on the contemporary music scene. He is also a wonderfully intelligent writer, as this important collection of essays amply demonstrates. The book is divided into three parts. ``The Shaping Imagination'' deals with questions of aesthetics and includes cogent analyses of some of Boulez's own music. ``Exemplars'' contains short sketches on composers and their music that Boulez finds worthwhilefrom Berlioz's Symphony Fantastique to the works of Messiaen. The short third section, ``Looking Back,'' contains tributes and brief essays of a more general nature. Though much of the writing is technical, the lay reader will still derive great pleasure from Boulez's lucid prose and articulate sentiments. Highly recommended. Larry Lipkis, Music Dept., Moravian Coll., Bethlehem, Pa.