Huangdi Neijing (), literally the Inner Canon of the Yellow Emperor or Esoteric Scripture of the Yellow Emperor, is an ancient Chinese medical text or group of texts that has been treated as a fundamental doctrinal source for Chinese medicine for more than two millennia. The work comprises two texts—each of eighty-one chapters or treatises in a question-and-answer format between the mythical Yellow Emperor and six of his equally legendary ministers. The first text, the Suwen (素問), also known as Basic Questions, covers the theoretical foundation of Chinese Medicine and its diagnostic methods. The second and generally less referred-to text, the Lingshu (靈樞; Spiritual Pivot), discusses acupuncture therapy in great detail. Collectively, these two texts are known as the Neijing or Huangdi Neijing. In practice, however, the title Neijing often refers only to the more influential Suwen. Two other texts also carried the prefix Huangdi Neijing in their titles: the Mingtang (明堂; Hall of Light) and the Taisu (太素; Grand Basis), both of which have survived only partially. The book was popular among Taoists. The earliest mention of the Huangdi Neijing was in the bibliographical chapter of the Hanshu 漢書 (or Book of Han, completed in 111 CE), next to a Huangdi Waijing 黃帝外經 (“Outer Canon of the Yellow Emperor”) that is now lost. A scholar-physician called Huangfu Mi 皇甫謐 (215-282 CE) was the first to claim that the Huangdi Neijing in 18 juan 卷 (or volumes) that was listed in the Hanshu bibliography corresponded with two different books that circulated in his own time: the Suwen and the Zhenjing 鍼經 (“Needling Canon”), each in 9 juan. Since scholars believe that Zhenjing was one of the Lingshu'''s earlier titles, they agree that the Han dynasty Huangdi Neijing was made of two different texts that are close in content to the works we know today as the Suwen and the Lingshu. The Yellow Emperor's Inner Classic (Huangdi Neijing, 黃帝內經) is the most important ancient text in Chinese medicine as well as a major book of Daoist theory and lifestyle.