one of three historical regions of Central Asia (the other two being Dbus-Gtsang and Khams) into which Tibet was once divided.

Between the 7th and 9th centuries CE, the Tibetan kingdom was extended until it reached the Tarim Basin to the north, China to the east, India and Nepal to the south, and the Kashmir region to the west. The newly added dominions to the east and northeast were called Mdo-Khams. The A-mdo region, constituting the northeastern part of ethnic Tibet, reached from the upper course of the Huang He (Yellow River) northeastward to Mchod-rten dkarpo (now in Gansu province, China). In the 1270s the area was taken and divided into different units by the Yuan (Mongol) dynasty (Yuan dynasty), and these passed to Qing (Qing dynasty) (Manchu) control in 1724 following the suppression of a Mongol revolt. A-mdo was officially incorporated into the Chinese provincial system, with the major portion of it becoming part of Qinghai (Tsinghai) province in 1928.