Austro-Asiatic Languages, important language family having two subfamilies: Munda, with 21 languages spoken in eastern India and Bangladesh; and Mon-Khmer, with nearly 150 languages spoken in Southeast Asia. Among Mon-Khmer languages are Khmer, the national language of Cambodia; Mon, a closely related language spoken in parts of Myanmar (formerly Burma) and Thailand; and Vietnamese. Austro comes from a Latin word for south; thus Austro-Asian languages are spoken in southern Asia.

The Munda languages are polysyllabic and differ from other Austro-Asiatic languages in their word formation and sentence structure (see Indian Languages). In the Mon-Khmer subfamily, Khmer and Mon have borrowed many words from the Indian languages Sanskrit and Pali. In the Viet-Muong branch of Mon-Khmer, Vietnamese was heavily influenced by Chinese; it is monosyllabic and has a complex tone system, as do other Viet-Muong languages. A few other Mon-Khmer languages have simple tone systems; much more common, however, are differentiations of vowel quality—breathy, creaky, or normal. Suffixes are not found in Mon-Khmer languages, but prefixes and infixes are common. In sentences, final particles may indicate the speaker’s attitude, and special modifiers called expressives convey images of colors, noises, and feelings. Some languages lack voiced stops such as g, d, and b. Words may end with palatized consonants such as ñ. Other distinctive sounds include imploded d and b, produced by suction of breath.

Mon and Khmer are written with Indian-derived alphabets. Vietnamese was written for centuries with modified Chinese characters. In 1910, however, a system was adopted that uses the Roman alphabet with additional signs; invented in 1650, it was the earliest writing system to notate tones, for which it uses accent marks.