Middle Chinese phonology is mainly based on the information from the phonological system of the Qièyùn 切韻, a rhyme dictionary compiled in 601. The literary standard represented by the Qièyùn and its later revisions served as the rhyming standard for centuries, even up until modern times. The phonological system of the Qièyùn as a rhyming standard is closely related to the imperial examination. In a country with many local dialects, a national standard had to be established for the examination. Once the phonological standard was established, it became almost impossible to change it in the context of the imperial examination for both the examinees and examiners. It is worth noting that unlike the phonology of Old Chinese, the categorical information of Middle Chinese has been thoroughly analyzed in the rhyme tables. The reconstruction of the phonetic values of the phonology of Middle Chinese was started in the early twentieth century by Western scholars, spearheaded by Bernard Karlgren’s Études sur la Phonologie Chinoise (1915–1926). In all the proposals of phonetic reconstructions, the categorical contrasts of the Qièyùn are strictly preserved and the phonological labels of the rhyme tables are consistently followed.