The official language of Laos is Lao, as spoken and written in Vientiane. As an official language it has successfully become the lingua franca between all Lao and non-Lao ethnic groups in Laos. Lao is a monosyllabic, tonal language but it contains many polysyllabic words borrowed from Indian, Pali and Sanskrit as well as words from Khmer. It has 6 tones, 33 consonants, and 28 vowels. Lao is also spoken in north-east Thailand and north Cambodia, which was originally part of the kingdom of Lan Xang. There are five main dialects in the country, each of which can be divided into further sub-dialects.

In colonial days French was introduced in the country and is still spoken in towns today, particularly by the older generation. Increasingly, the government is using English and the younger generation in the towns are also learning to speak English.