Fanqie is a method used in traditional Chinese lexicography to indicate the pronunciation of a monosyllabic character by using two other characters, one with the same initial consonant as the desired syllable and one in which the rest of the syllable (the final) matches. The method was introduced in the 3rd century AD and is to some extent still used in commentaries on the classics and dictionaries.

Early dictionaries such as the Erya (3rd century BC) did not indicate pronunciation. One of the innovations of the Shuowen Jiezi (early 2nd century AD) was to indicate the pronunciation of a character by the dúruò (讀若, 'read as') method, giving another character with the same pronunciation. The introduction of Buddhism to China around the 1st century brought Indian phonetic knowledge, which may have inspired the idea of fanqie. According to the 6th-century scholar Yan Zhitui, fanqie were first used by Sun Yan (孫炎), of the state of Wei during the Three Kingdoms period (220–280 AD), in his Erya Yinyi (爾雅音義, "Sounds and Meanings of Erya"). However, earlier examples have been found in the late-2nd-century works of Fu Qian and Ying Shao.

The oldest extant sources of significant bodies of fanqie are fragments of the original Yupian (544 AD) found in Japan and the Jingdian Shiwen, a commentary on the classics that was written in 583 AD. The method was used throughout the Qieyun, a Chinese rhyme dictionary published in 601 AD during the Sui dynasty. When Classical Chinese poetry flowered during the Tang dynasty, the Qieyun became the authoritative source for literary pronunciations. Several revisions and enlargements were produced, the most important of which was the Guangyun (1007–1008). Even after the more sophisticated rime table analysis was developed, fanqie continued to be used in dictionaries, including the voluminous Kangxi Dictionary, published in 1716, and the Ciyuan and Cihai of the 1930s.

During the Qing dynasty, some bilingual Chinese-Manchu dictionaries had the Manchu words phonetically transcribed with Chinese characters. The book 御製增訂清文鑑 ("Imperially Published Revised and Enlarged Mirror of Qing"), in both Manchu and Chinese, used Manchu script to transcribe Chinese words and Chinese characters to transcribe Manchu words by using fanqie.

In the fanqie method, a character's pronunciation is represented by two other characters. The onset (initial consonant) is represented by that of the first of the two characters (上字 'upper word', as Chinese was written vertically); the final (including the medial glide, the nuclear vowel and the coda) and the tone are represented by those of the second of the two characters (下字, 'lower word'). For example, in the Qieyun, the character 東 is described by the formula 德紅反. The first two characters indicate the onset and the final, respectively, and so the pronunciation of 東 [tuŋ] is given as the onset [t] of 德 [tək] with the final [uŋ] of 紅 [ɣuŋ], with the same tone as 紅.

In the rhyme dictionaries, there was a tendency to choose pairs of characters that agree on the presence or absence of a palatal medial -j-, but there was no such tendency for the rounded medial -w-, which was represented solely in the final character. There was also a strong tendency to spell words with labial initials using final characters with labial initials.

The third character 反 fǎn 'turn back' is the usual marker of a fanqie spelling in the Qieyun. In later dictionaries such as the Guangyun, the marker character is 切 qiè 'run together'. (The commonly-cited reading 'cut' seems to be modern.) The Qing scholar Gu Yanwu suggested that fǎn, which also meant 'overthrow', was avoided after the devastating rebellions during the middle of the Tang dynasty. The origin of both terms is obscure. The compound word fǎnqiè first appeared during the Song dynasty.

Fanqie provide information about the sounds of earlier forms of Chinese, but its recovery is not straightforward. Several characters could be used for each initial or final, and no character was ever used to spell itself.