Yuejing 樂經, the "Classic of Music", is the putative title of a book that was once counted amoung the "six classics" (liujing 六經) or "six arts" (liuyi 六藝). A chapter of the philosophical treatise Xunzi 荀子, Yuelun 樂論, proves that at least in the state of Qi 齊 a "discipline" of music existed among the knowledgeable "skills" of scholars.
The chapter on music in the official dynastic history Songshu 宋書 (19-22 Yue zhi 樂志) explains that the Yuejing was lost during the literary inquisition under the First Emperor of Qin 秦始皇帝 (r. 247-210 BCE). This assumption is based on a statement in the history Houhanji 後漢記, and was also adopted in the literary critique Wenxin diaolong 文心雕龍 by Liu Xie 劉勰. It is nevertheless believed that there existed indeed such a book during the Han period 漢 (206 BCE-220 CE).
Wang Yinglin 王應麟 (1223-1296), a late Song period 宋 (960-1279) scholar and author of the Kunxue jiwen 困學紀聞, maintained that in 4 CE a "professorship" (boshi 博士) was founded for this classic, while the introduction to the music section in the descriptive bibliography Siku quanshu zongmu tiyao 四庫全書總目提要 explains that the Yuejing used during that time was a new text, and not the ancient Yuejing.
Fan Wenlan 范文瀾 (1893-1969) shows that already in the early Former Han period 前漢 (206 BCE-8 CE), experts in ritual music were active at the imperial court. During the reign of Emperor Wen 漢文帝 (180 – 157 BCE), a certain Dou Gong 竇公 presented a book on music that was found to be identical with the chapter Dasiyue 大司樂 on the "Musician-in-chief" in the Classic Zhouli 周禮.
The Ming period 明 (1368-1644) scholar Ke Shangqian 柯尚遷 (1500-1582) assumed that the Yuejing was identical to this chapter, a statement repeated in Zhang Fengxiang's 張鳳翔 (1473-1501) Yuejing jizhu 樂經集注. Another prove for the non-existence of a classic of music is Emperor Wu's 漢武帝 (r. 141 -87 BCE) appointment of "professors" for but five disciplines, and not for the sixth discipline of music.
Some authors, like the great Ming period musical theoretician Zhu Zaiyu 朱載堉 (1536 -1610), or the Qing period 清 (1644-1911) philosopher Zhu Yizun 朱彝尊 (1629-1709), believed that the Yuejing was identical to the "Book of Songs" Shijing 詩經 (or the Zhouli chapter). Shan Jia 山佳 discovered two manuscript versions of an ancient text called Yuejing or Gu yuejing 古樂經, both included in the rare collectanea Qingzhaotang congshu xubian 青照堂叢書續編 from 1835. The compiler of the Gu yuejing, Wen Yingxiong 文應熊 (1638-1719), explains in the preface that he came into the possession of this very old text on music in 1703. The book of 3 juan explains the system of the twelve pitchpipes, the eight styles of music and the eight types of musical instruments.
Yet there is also some evidence that before the Qin period 秦 (221-206 BCE) a book called Yue had in fact existed. Liu Quanzhi 劉全志 demonstrates how important music was at the courts of the regional rulers of the Spring and Autumn 春秋 (770-5th cent. BCE) and the Warring States 戰國 (5th cent.-221 BCE) periods, and that the music masters relied on written sources for performance. He follows an earlier idea of Liao Ping 廖平, author of the Yuejing fanli 樂經凡例, who ascertained that music was in fact one of the "six skills" of rituals.
An excellent overview of the discourse is given by Tian Jun 田君. He sums up that there were three different interpretations, the first assuming that were was never a separate text called Yuejing. The topic of music was covered by the books Shijing or Liji 禮記, or by both. The second "school" assumed that the original book on the royal music of the Zhou dynasty 周 (11th cent.-221 BCE) was lost, either because the regional rulers illegally adopted the royal rituals described in it, or because the ancient rites became obsolete, or because of the "book burning" or literary inquisition of the Qin. The third group of scholars assumes that the text survives either in the chapter Dayuesi of the Zhouli or the Yueji 樂記 in the ritual classic Liji, or in various other texts on music.
Seven fragments of a book called Yuejing (whether it was the ancient one or a text written during the Han period) quoted in other texts were collected by the Qing period scholar Wang Mo 王謨 (juren degree 1768). They are included in Mo's collectanea Han-Wei yishu chao 漢魏遺書抄. Wang Fu 汪紱 (1592-1752) had compiled a first compilation of texts on ancient music, as a kind of "reconstruction" of the ancient Yuejing, the Yuejing huowen 樂經或問 of 3 juan.