Tanintharyi, better known by the old name Tenasserim, is a division of Myanmar, covering the long narrow southern part of the country on the Kra Isthmus. It borders the Andaman Sea to the west and Thailand to the east. To the north is the Mon State. The capital of the division is Tavoy (Dawei). The other main city is Mergui.

The division covers an area of 43,328 km², and in the 1983 census it had a population of 917,628. The division is sub-divided into 5 districts: Amherst, Mergui, Tavoy, Thaton, Toungoo. The ISO 3166-2 code for the division is MM-05.

Historically the area belonged to the Burmese kingdom for most of the time, but was also sometimes a tributary of the Thai kingdoms of Sukhothai and Ayutthaya. At the end of the First Burmese War in 1826 Tenasserim became part of the British colonial empire with the Treaty of Yandaboo. It was then part of Lower Burma.

With the independence of Burma in 1948 the northeastern part of Tenasserim became the Karen state (now named Kayin). In 1974 the Mon state was created, taking the northwestern part of Tenasserim. As the previous capital Moulmein is in the Mon state, the capital of Tenasserim was moved to Tavoy. In 1989 the division was officially renamed to Tanintharyi.