The Akhak kwebŏm, the most comprehensive Korean musical treatise of the early Yi dynasty, was compiled in 1493 by a team headed by Song Hyŏn (1439–1504) and other editors, at the order of King Sŏngjong (ruled 1469–1494). Consisting of nine chapters (kwŏn or chüan) in three fascicles, the treatise describes and classifies musical instruments (for aak, tangak, and hyangak), musical theory, sacrificial and ritual music, costumes and ceremonial accessories for court musicians and dancers, and tangak and hyangak court dances (chŏngjae), including dancing and singing. It is an invaluable source not only for the study of Korean music theory and history, but also for the study of Korean dance, literature, and language.