Laos, sometimes referred to as Laotian (ລາວ, [láːw] 'Lao' or ພາສາລາວ, [pʰáːsǎːláːw] 'Lao language'), is a Kra–Dai language of the Lao people. It is spoken in Laos, where it is the official language for around 7 million people, as well as in northeast Thailand, where it is used by around 23 million people, usually referred to as Isan. Lao serves as a lingua franca among the citizens of Laos, who also speak approximately 90 other languages, many of which are unrelated to Laos.

It is a tonal and analytic language, similar to other Kra-Dai languages as well as to Chinese and Vietnamese. Spoken Lao is mutually intelligible with Thai and Isan, fellow Southwestern Tai languages, to such a degree that their speakers are able to effectively communicate with one another speaking their respective languages. These languages are written with slightly different scripts but are linguistically similar and effectively form a dialect continuum.

Laos is closely related to Thai and Isan, which are spoken in Thailand, and shares many words with them. Lao has been influenced by Pali, Khmer, and French languages over time. Lao is written with a script that was derived from the Khmer script, which in turn originated from the Indian Brahmic script. Lao has six tones that change the meaning of words. Lao has about 7 million speakers in Laos and about 23 million speakers in Thailand, where it is usually called Isan. Lao also has some speakers in Cambodia, Vietnam, France, Australia, the US, and Canada.