Vietnamese is spoken in Vietnam by about 70 million people. Its linguistic affiliation has long been a matter of debate. It is now throught by most to belong to the Mon-Khmer family of languages which includes Khmer （Cambodian）, but this is not entirely certain. The only language closely related to Vietnamese is Muong, spoken in northern Vietnam.

　　VIetnam was ruled by China until the middle of the 10th century. So many Chinese words entered the language that Vietnamese was long thought to be related to Chinese. It was written using the Chinese characters until the 17th century, when Catholic missionaries devised a Roman-based orthography. It contains a complex system of diacritical marks, some distinguishing certain vowel sounds, others indicating tone. As can be seen in some of the lines above, a letter may often contain two diacritical marks.

　　The Tale of Kieu, the Vietnamese national poem, was written by Nguyen Du in the early 19th century. It is 3,254 lines in length； educated Vietnamese know most of them by heart.