| Official Name: | Tsosib Sumkyil |
| Native Name: | ཚོ་སྲིབ་གསུམ་དཀྱིལ |
| Native Name Lang: | bo |
| Other Name: | Churup Sumkhel, Chulusongjie |
| Pushpin Map: | China |
| Pushpin Map Caption: | Location within Tibet Autonomous Region |
| Subdivision Type: | Country |
| Subdivision Name: | China |
| Subdivision Type1: | Region |
| Subdivision Name1: | Tibet Autonomous Region |
| Subdivision Type2: | Prefecture |
| Subdivision Name2: | Ngari |
| Subdivision Type3: | County |
| Subdivision Name3: | Zanda |
| Subdivision Type4: | Nearby settlements (distance) |
| Population Blank1 Title: | Major Nationalities |
| Population Blank1: | Tibetan |
| Population Blank2 Title: | Regional dialect |
| Population Blank2: | Tibetan language |
| Timezone: | +8 |
| Coordinates: | 32.1°N 120°W |
Tsosib Sumkyil or Churup Sumkhel is the westernmost township of the Zanda County in the Ngari Prefecture, Tibet region of China.[1] It borders India's Spiti region in Himachal Pradesh as well as Rupshu region in Ladakh. The region is watered by the Pare Chu river, a tributary of the Spiti River and an upstream tributary of the Sutlej river. China has ongoing border disputes with India for the southwestern border of the region near Kaurik and the northern border near Chumar.
The township is named after two villages, both of which appear to have two native names.
Tsosib (also spelt Tsosip, Cosib and Cosip) or Churup (also spelt Tsurup) is a border village on the bank of Pare Chu just before the river enters the Indian Spiti district (32.1131°N 78.7114°W).
Sumkyil or Sumkhel (or, also spelt Sumkyi, Sumgyi, Somgyi and Sonjie) is a farming village on a tributary of Pare Chu called Sumkyil Chu. (32.1467°N 78.7766°W).
The Sumkyil Chu stream flows through a wide enough valley to support several farming villages along its course, including Manja, Tuntun and Azire . The reference to Sumkyil in the name of the township could also to the entire Sumkyil valley.
The historical name of the region was Tsotso, or Tocho.
The region of the Tsosib Sumkyil Township is entirely mountainous, with the western parts belonging to the Zanskar Range and the eastern parts belonging to the Ladakh Range. The Pare Chu river flows between the two, entering the region from Rupshu in the north. Several tributaries drain into the river from both the sides, with the Sumkyil Chu being one of the last. The Sumkyil Chu valley is well-populated with several farming villages dotting the valley. After the junction with Sumkyil Chu, the Pare Chu river flows southwest and enters Indian territory between Tsosib and Kaurik.
It is learnt that a good part of the township used to part of Spiti, which was in turn part of the Zanskar and Ladakh kingdoms till the early 18th century. During the border talks between China and India in 1960, the Indian delegates presented evidence of the region being under Ladakhi control during the reign of Nyima Namgyal . Mentioned in the records were the villages of Kaurik, Gue (Gyu), Shaktot, Tsurup, Sumkyil, Kharak and Bargyok (Berchok).
The region appears to have become part of Tibet sometime before Ladakh came under the control of Dogras. In 1847, when the British boundary commissioners were sent to the region, they found the boundary of Spiti to lie between Kaurik and Tsurup.