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 Ikhwan al-Safa?, Ibn Sina, Ibn Zayla, al-Katib, Ibn al-Tahhan, al-Tifashi, and the ground breaking works of al-Urmawi with his novel circular notation that survived up to the 20th century. They also include the works of al-Maraghi who invented many long rhythmic modes, and the works of al-Shirwani, al-Ladh9qi and Awbahi. The work summarizes the definition of all the rhythmic modes in alphabetical listing.