Lao or Laotian is a tonal language of the Kradai language family. It is the official language of Laos, and also spoken in the northeast of Thailand, where it is usually referred to as the Isan language. Being the primary language of the Lao people, Lao is also an important second language for the multitude of ethnic groups in Laos and in Isan. Lao, like all languages in Laos, is written in an abugida script. Although there is no official standard, the Vientiane dialect has become the de facto standard. The Lao language has numerous dialects, but they are mutually intelligible. The Isan language can also be further sub-divided into various dialects, but they too remain mutually intelligible with the Lao dialects of Laos and are regarded as a cohesive identity. In addition to the following dialects, there are numerous small dialects spoken by tribes descended from forced Lao migrations to Central Thailand.  

• Vientiane Lao
• Northern Lao (Luang Prabang)
• North-Eastern Lao (Xieng Khouang)
• Central Lao (Khammouan)
• Southern Lao (Champasak)
• Isan Lao (Isan) (sometimes considered a separate language for political reasons, but spoken by ethnic Lao)

In addition to the dialects of the Lao languages, numerous closely related languages (or dialects, depending on the classification) are spoken throughout the Lao-speaking realm in Laos and Thailand, such as the Nyaw, Phu Thai, Saek, Lao Wieng, Tai Dam, Tai Daeng, etc. These Tai peoples are classified by the Lao government as Lao Loum or lowland Lao. Lao and Thai are also very similar and share most of their basic vocabulary, but differences in many basic words limit inter-comprehension.

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