The Book for the Completion of Musical Knowledge is one of two unique treatises coming down to us from the 11th century; the other is Encompasser of the Arts of Ibn al- ?a???n al-M?s?q?. Both are written by practicing musicians and composers, and as such provide, a most welcome musical practices supplement to the tenth-century legacy of music theory and literature, namely, the works of al-F?r?b? and al-I?fah?n?. In composition, al-K?tib provides useful details regarding the process to set a poem to music; in education, he advises students on how to choose a good teacher; in performance, he advises students about to breathe properly and how to ornament vocal and instrumental music.