This book provides the first comprehensive description of the phonology and phonetics of Standard Mongolian, known as the Halh (Khalkha) dialect and spoken in Ulaanbaatar, the capital of the Republic of Mongolia; and the first account in any language of the historical phonology of the Mongolian group of languages. The synchronic phonology is based on data collected by the authors and on their own phonological analyses. The historical phonology is based on their research on the Halh, on published Chinese and Mongolian sources for the modern Mongolic languages, and on their reconstruction of Old Mongolian from the medieval written sources.