A musical practice used for centuries the world over, improvisation too often has been neglected by scholars who dismiss it as either technically undissectible or inexplicably mysterious. At different times and in different cultures, performing music that is not "precomposed" has constituted an artful expression of the performer's individuality (the Baroque); a wild, unthinking form of expression (jazz antagonists); and the best method to train inexperienced musicians to use their instruments (the Middle East). This wide-ranging collection of essays considers musical improvisation from a...