The book deals with rhythmic theories and practices in Arabic and Persian sources from the 10th to the 15th century. Sources prior to the 10th century are summarized as a basis for the theories that follow from the 10th to the 15th century. They include the works of Ikhwān al-Ṣafāʾ, Ibn Sīnā, Ibn Zayla, al-Kātib, Ibn al-Ṭaḥḥān, al-Tīfāshī, and the ground breaking works of al-Urmawī with his novel circular notation that survived up to the 20th century. They also include the works of al-Marāghī who invented many long rhythmic modes, and the works of al-Shirwānī, al-Lādh9qī and Awbahī. The work summarizes the definition of all the rhythmic modes in alphabetical listing.