Lao or Laotian (, BGN/PCGN: phasa lao, ) is a tonal language of the Tai–Kadai 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.