This book presents a description of the grammar of Zhoutun, an endangered Sinitic variety spoken by less than 1000 people in the Qinghai Province of northwest China. With vocabulary predominantly from Chinese and Tibetan syntax, Zhoutun is one of the Sinitic varieties most distant from Standard Chinese, with unexpected typological features like, for example, case markers, rigid SOV word order, simplified tonal system, negative copula as a disjunctive coordinator and "locutor-referential pronoun" which is not found in Chinese and in many languages. Zhoutun is also a representative variety of the Gansu-Qinghai linguistic area in which Mongolic and Turkic languages coexist with Tibetan and Chinese dialects from a long time. This book also describes the sociolinguistic and sociohistorical contexts of Zhoutun. It should be of interest to specialists and students of language contact, linguistic typology, Chinese dialectology, language geography, anthropological linguistics, sociolinguistics, folklore studies, and preservation of endangered languages.