Old Chinese refers to the Chinese language before the Qin dynasty (Mandarin: xiānqín 先秦). Unlike later periods, there is no systematic record of an entire phonology. The phonology of Old Chinese must be completely reconstructed, based on various pieces of unrelated source materials. The reconstruction of Old Chinese represents the most difficult work in the study of the Chinese historical phonology. It also should be noted that the source materials often have unclear information regarding the time and geographical locations about the language. The source materials mainly include the rhyming words of ancient poetry, the Chinese characters that share phonetic components, and reconstructions based on both the phonology of Middle Chinese, which is itself based on rhyme dictionaries with complete phonological information, and the pronunciation of modern Chinese dialects. Although Old Chinese phonology must appear first according to chronology, it would be very helpful to read Part III (Middle Chinese) first before coming back to read this part, as linguists studying Old Chinese use Middle Chinese phonology as their main reference point in the reconstruction of phonology. A good understanding of Middle Chinese phonology, and especially the terminologies involved, will benefit the reading of this part.