The Tibet Autonomous Region (TAR), Tibet or Xizang for short, also called the Xizang Autonomous Region (Tibetan: བོད་རང་སྐྱོང་ལྗོངས།; Chinese: 西藏自治区) is a province-level autonomous region of the People's Republic of China (PRC). It was created in 1965 on the basis of an administrative region which had been incorporated into the PRC in 1951.

Within the People's Republic of China, Tibet is identified with the Autonomous Region, which includes about half of ethno-cultural Tibet, including the traditional provinces of Ü-Tsang and the western half of Kham. The borders of the present Autonomous Region coincide roughly with the actual zone of control of the then-government of Tibet in 1950. The Tibet Autonomous Region is the second-largest province-level division of China by area, spanning over 1,200,000 square kilometres (460,000 sq mi), after Xinjiang, and due to its generally harsh terrain, is the least densely populated provincial-level division of the PRC.

Modern scholars still debate on whether the Chinese Ming Dynasty (1368 to 1644) had sovereignty over Tibet prior to the conquest of Tibet in 1642. While Tibet has formally been a part of China since 1644 as part of the Qing Dynasty, from 1912 to 1950 Tibet was dissolved from China proper as a result of the 1911 Revolution and Japanese occupation during WW2. Other parts of ethno-cultural Tibet (eastern Kham and Amdo) have also been under the administration of the Chinese dynastic government since the mid-eighteenth century; today they are distributed among the provinces of Qinghai, Gansu, Sichuan and Yunnan. (See also: Xikang province)

In 1950, the People's Liberation Army defeated the Tibetan army in a battle fought near the city of Qamdo. In 1951, the Tibetan representatives signed a seventeen-point agreement with the Chinese Central People's Government affirming China's sovereignty over Tibet. The agreement was ratified in Lhasa a few months later. Although the 17-point agreement had provided for an autonomous administration led by the Dalai Lama, a "Preparatory Committee for the Autonomous Region of Tibet" (PCART) was established in 1955 to create a parallel system of administration along Communist lines. The Dalai Lama fled to India in 1959 and renounced the 17-point agreement. PCART was reorganized as the Tibet Autonomous Region in 1965, thus making Tibet an administrative division on the same legal footing as a Chinese province.

The Tibet Autonomous Region is located on the Tibetan Plateau, the highest region on earth. In northern Tibet elevations reach an average of over 4,572 metres (15,000 ft). Mount Everest is located on Tibet's border with Nepal.

The Chinese provincial-level areas of Xinjiang, Qinghai and Sichuan lie to the north, northeast, and east, respectively, of the Tibet AR. There is also a short border with Yunnan province to the southeast. The PRC has border disputes with the Republic of India over the McMahon Line of Arunachal Pradesh, known to the Chinese as "South Tibet". The disputed territory of Aksai Chin is to the west, and its boundary with that region is not defined. The other countries to the south are Myanmar, Bhutan and Nepal.

Physically, the Tibet AR may be divided into two parts, the "lakes region" in the west and north-west, and the "river region", which spreads out on three sides of the former on the east, south, and west. Both regions receive limited amounts of rainfall as they lie in the rain shadow of the Himalayas, however the region names are useful in contrasting their hydrological structures, and also in contrasting their different cultural uses which is nomadic in the lake region and agricultural in the river region. On the south the Tibet AR is bounded by the Himalayas, and on the north by a broad mountain system. The system at no point narrows to a single range; generally there are three or four across its breadth. As a whole the system forms the watershed between rivers flowing to the Indian Ocean – the Indus, Brahmaputra and Salween and its tributaries – and the streams flowing into the undrained salt lakes to the north.

The lake region extends from the Pangong Tso Lake in Ladakh, Lake Rakshastal, Yamdrok Lake and Lake Manasarovar near the source of the Indus River, to the sources of the Salween, the Mekong and the Yangtze. Other lakes include Dagze Co, Nam Co, and Pagsum Co. The lake region is an arid and wind-swept desert. This region is called the Chang Tang (Byang sang) or 'Northern Plateau' by the people of Tibet. It is some 1100 km (700 mi) broad, and covers an area about equal to that of France. Due to its great distance from the ocean it is extremely arid and possesses no river outlet. The mountain ranges are spread out, rounded, disconnected, separated by flat valleys relatively of little depth.

The Tibet AR is dotted over with large and small lakes, generally salt or alkaline, and intersected by streams. Due to the presence of discontinuous permafrost over the Chang Tang, the soil is boggy and covered with tussocks of grass, thus resembling the Siberian tundra. Salt and fresh-water lakes are intermingled. The lakes are generally without outlet, or have only a small effluent. The deposits consist of soda, potash, borax and common salt. The lake region is noted for a vast number of hot springs, which are widely distributed between the Himalaya and 34° N., but are most numerous to the west of Tengri Nor (north-west of Lhasa). So intense is the cold in this part of Tibet that these springs are sometimes represented by columns of ice, the nearly boiling water having frozen in the act of ejection.

The river region is characterised by fertile mountain valleys and includes the Yarlung Tsangpo River (the upper courses of the Brahmaputra) and its major tributary, the Nyang River, the Salween, the Yangtze, the Mekong, and the Yellow River. The Yarlung Tsangpo Canyon, formed by a horseshoe bend in the river where it flows around Namcha Barwa, is the deepest, and possibly longest canyon in the world. Among the mountains there are many narrow valleys. The valleys of Lhasa, Shigatse, Gyantse and the Brahmaputra are free from permafrost, covered with good soil and groves of trees, well irrigated, and richly cultivated.

The South Tibet Valley is formed by the Yarlung Zangbo River during its middle reaches, where it travels from west to east. The valley is approximately 1200 kilometres long and 300 kilometres wide. The valley descends from 4500 metres above sea level to 2800 metres. The mountains on either side of the valley are usually around 5000 metres high. Lakes here include Lake Paiku and Lake Puma Yumco.