Historical Chinese phonology deals with reconstructing the sounds of from the past. As is written with , not alphabetic or syllabary, the methods employed in Historical Chinese phonology differ considerably from those employed in, for example, linguistics.
Chinese scholars, especially those in the Qing Dynasty including Duan Yucai, studied the sound system and sounds of and Old Chinese for years. Based on their results, and armed with his knowledge of Western historical linguistics, the sinologist Bernhard Karlgren reconstructed the sounds of ancient Chinese with Latin alphabet for the first time during the early 20th century. Walter Simon and Henri Maspero also made great contributions in the field during the early days of its development.
The reconstruction of Middle Chinese draws its data from:
* and rime tables of the Middle Chinese era, such as ''Guangyun''
*modern Chinese speaking variants such as Cantonese, , , , & etc.
*Chinese loanwords in other languages such as , and
*the from other languages such as Sanskrit and into Chinese
Insight to the phonology of this era was further gained with the discovery of the fragmentary ''Qieyun'' in the Dunhuang Caves in the 1930s. The work had earlier been considered lost. Karlgren, who based his work on much later rime dictionaries, suggested that Middle Chinese was a live language of the - period. Today, this notion has been replaced by the view that the sound system in ''Qieyun'' represents the literate reading adopted by the literate class of the period throughout the country, not any live language that once existed.
The reconstruction of Old Chinese is more controversial than that of Middle Chinese since it has to be extrapolated from the Middle Chinese data. Phonological information concerning Old Chinese are chiefly gained from:
*the rhymed texts written before the Qin Dynasty, chiefly '''', the earliest anthology of Chinese poetry
*the fact that were homophones or near-homophones when the characters were first created.
Today the reconstruction of Old Chinese is carried out in the light of linguistics.