Theinni or Hsenwi (Shan: သႅၼ်ဝီ; Burmese: သိန္နီ, pronounced [θèiɰ̃nì]; Thai: แสนหวี, RTGS: Saen Wi, pronounced [sɛ̌ːn wǐː]) is a town in northern Shan State of Burma, situated near the north bank of the Nam Tu River and now the centre of Hsenwi Township in Lashio District.

Numerous rebellions and civil wars reduced Theinni from its position as arguably the most powerful and populous Shan state to what is perceived as a condition of fearful desolation.

[5] It is de jure a part of Burma, but is currently controlled by the Brotherhood Alliance as of 30 October 2023 as a result of the 2021–2023 Myanmar civil war.

These had, however, fallen away in Burmese times, and before the British annexation, Theinni was divided into five parts by name; but there was no central authority, and the whole state was in hopeless disorder.

[5][1] The northern part of North Theinni is a mass of hills affected by the geological fault which has produced the rift that forms the Nam Tu or Myitnge valley, and has thrown up a series of parallel ranges which extend northwards to the Shweli River (Lung Kiang), without altogether destroying the north and south trend which is the characteristic of the Shan hills as a whole.

In the valleys between these hills are numerous tracts under rice cultivation, some circular or oval, some mere ribands along the river banks.

A range running westwards from the Salween, and marking the southern border of the rift in the hills, divides North from South Theinni.

Apart from this it consists of broken hill-country of no great height, or open rolling downs, the latter chiefly in the eastern half of the state.

In the plains of the uplands there are yearly frosts in January, February and March, but in the greater part of the state the thermometer rarely falls to freezing-point, and in the hot weather does not exceed ninety degrees for any length of time.