the southernmost region of The Sudan (Sudan, The). It is bounded by Ethiopia to the east, Kenya to the southeast, Uganda and Congo (Kinshasa) to the south, and the Central African Republic to the west.

Al-Istiwāʾīyah is geographically isolated from the rest of The Sudan by the vast swamps of As-Sudd (Sudd, Al-) to the north and by intermontane rainforests that cover the southernmost part of the country. The Imatong and Dongotona mountains rise along the border with Uganda and dominate the eastern part of the region. The Imatongs are in fact the highest mountains in The Sudan, with Mount Kinyeti the country's highest peak at 10,456 feet (3,187 metres). They are covered with lush rainforests, and their drainage forms extensive swamps to the north. The Al-Jabal River, or Mountain Nile, flows northward through east-central Al-Istiwāʾīyah. To the west, the highlands are drained northward by the Yei, Ibba, and Sue rivers. The Marra and Abū Gatta hills dominate the westernmost part of the region.

Al-Istiwāʾīyah is inhabited by various peoples who practice traditional African religions or Christianity and who speak Eastern Sudanic or Adamawa-Ubangi languages (belonging to the Nilo-Saharan and Niger-Congo language families, respectively). The Zande are the largest single ethnic group in Al-Istiwāʾīyah and dominate its western portion. Among the peoples in the centre and east are the Murle, Didinga, Bari, Kuku, Kakwa, Bongo, and Baka, among others. There are few Muslims in the region.

Agriculture is the principal occupation, and sedentary and shifting cultivation produce wheat, durra (sorghum), sesame, cotton, coffee, tobacco, corn (maize), hemp, jute, castor-oil seeds, pulses, and root crops. The lumber industry yields such products as firewood, charcoal, agricultural implements, railway ties, telegraph poles, rope fibres, and tanning materials. This industry has been periodically interrupted by civil war with the north, however. Other industries are rudimentary and are basically restricted to the production of milled flour and processed foods. Juba is the chief town and administrative and commercial centre of the region. Other towns include Yambio, Yei, and Amadi.

Al-Istiwāʾīyah formed part of the region conquered by Egypt in 1821. The area's traditional trade was in slaves and ivory, which were sent north to the Arabic-speaking portions of the region and thence to Egypt. The Anglo-Egyptian government tried unsuccessfully to suppress the slave trade in the early 1870s, and the first attempts to spread Christianity (through mission schools) were also undertaken. During the 1880s most of the area was in the hands of the Mahdists (i.e., supporters of al-Mahdī, a Muslim religious reformer who had undertaken a revolt against British rule beginning in 1881). The region was seized by Anglo-Egyptian forces in 1898, and their rule continued until The Sudan gained independence in 1956.

Al-Istiwāʾīyah's history since then has been one of conflict with the Muslim, Arabic-speaking majority of central and northern Sudan, which dominates the central government. Agreements on regional autonomy for Al-Istiwāʾīyah and neighbouring regions have repeatedly fallen apart, and the central government's periodic attempts to Islamize the south have provoked deep resentment and armed resistance; a rebellion by southern troops at Juba in 1958 led to a civil war that continued until 1969. The north-south civil war that erupted again in 1983 and was still being fought at the end of the 20th century further disrupted Al-Istiwāʾīyah's economy and turned many of its people into refugees.