Pierre Boulez discovered Paul Klee in 1947, during the first Avignon Festival, and his subsequent contact with his work and writings only reinforced his fascination with the artist, whose method and reflections seemed to reflect his own concerns. This book is a testament to this deep and persistent admiration: leaving aside the commonplaces about the influence of music on Klee's work, Boulez offers the reader an enriching analysis of the different theoretical approaches that accompany the creative process in various arts and that can be useful to other artists. An invaluable master class that transcends eras and disciplines, illustrated with more than sixty examples of the painter's fascinating work.