Laos–Thailand relations

Laos and Thailand have had bilateral relations since the time of their precursor Lan Xang and Ayutthaya kingdoms in the 15th century. The two countries share a border and express linguistic and cultural similarities. The Lao kingdom of Lan Xang included all of northeastern Thailand as recently as the early 18th century. Thailand's northeastern region, Isan, has particularly strong Lao roots. Linguistically, the inhabitants of Isan, a third of the Thai population, speak the Isan language, a Lao dialect. Diplomacy has concentrated on the Mekong River, seeking to make it a "river of true peace and friendship", as made explicit in statements by both respective prime ministers in 1976.

Diplomatic relations between the modern states were established in 1950, but cross-border cooperation began at the end of the Cold War.