Adal (Harari: ኣው አብዳል/ኢዳል; Somali: Awdal), also known as Aw Idal, Awdal, or Aw Abdal was a historical Muslim region in the Horn of Africa. Located east of Ifat and the Awash river as far as the coast, and including Harar as well as Zeila. The Zeila state often denoted Adal and other Muslim dominions in medieval texts.

Adal was situated east of the province of Ifat and was a general term for a region inhabited by Muslims. According to Portuguese explorer Francisco Alvarez, Adal in 1520 bordered on the Abyssinian frontier province of Fatagar in the west and stretched to Cape Guardafui in the east. He further stated that it was confined by the Kingdom of Dankali in the north west and that the leaders of Adal were considered saints by the locals for their warfare with neighboring Abyssinia.

It was used ambiguously in the medieval era to indicate the Muslim inhabitant low land portion east of the Ethiopian Empire. Including north of the Awash River towards Lake Abbe in modern Djibouti–Ethiopia border as well as the territory between Shewa and Zeila to the northwest of Somalia. In addition to Zeila, Leo Africanus also identified the coastal ports of Berbera and Maydh as lying within the dominion of Adal. Districts within Adal included Hubat, Gidaya and Hargaya. It also occasionally included the Hadiya Sultanate.

According to Ewald Wagner, the Adal region was historically the area stretching from Zeila to Harar. In the 1800s Catholic missionary Stanely states Adal is situated west of Zeila. In 1885, French trader Alfred Barday noted that the Adal grassland, which extended to the Awash River, was 'Banan Herer' (Harar plateau) in Somali. Dr. Duri Mohammed asserts the lowlands outside the city of Harar is known as Aw Abdal where Imams traditionally led prayer. According to Amélie Chekroun, Adal designated the region east of the Awash River, replacing Ifat as the Muslim power which had come under Ethiopian Christian control in the 1300s. The Christian state under Menelik II's invasion during the 1800s for the first time in its history maintained control in Adal therefore incorporating it into modern Ethiopia. The region was mostly located in modern-day Awdal and had Zeila as a capital city but also controlled other interior towns like Abasa or Dakkar extending into the Harar plateau to the south-east and modern day Djibouti in the west.

Eidal (Abdal) becomes Emir of the region succeeding saint Barkhadle in AD 1067 following a victory against a Persian.

After two days he sent some of the horsemen to Hararge to the Sarif Idal, and (this) came (to him) with 150 horsemen. He and the Imam started the war against the army of al-Kanis Mari in the land of Bissidimo. The war broke out for four days until they reached the land of Kurummi. When Sarif Idal reached her, he cut off her head and hung her on lances. She had 200 riders with her, all of whom God quickly sent into the fire of hell. The Imam returned (with) Sarif Idal after killing her and was called Emir Idal. He entered Hararge with 500 riders, praising God and cheering with innumerable and incalculable booty.

— Yahya Nasrallah, Fath Madinat Harar

Islam was first introduced to the area early on from the Arabian Peninsula, shortly after the Hijrah. Zeila's two-mihrab Masjid al-Qiblatayn dates to the 7th century, and is one of the oldest mosques in the world. The earliest reference to Adal was following the collapse of the Makhzumi dynasty in July 1288 when 'Ali Baziyu led a campaign in Adal and Mora which was concluded by the killing of the lords of Adal and Mora, the victorious Sultan then annexed Adal and Mora to his Kingdom. Adal is also mentioned by Marco Polo in 1295 as a state continuously in conflict with Abyssinia. Ongoing religious tensions and occasional military clashes were a feature of the relationship between the Muslims and their Christian neighbours. Marco Polo, recounted the story of an Ethiopian bishop who was abducted by an Islamic leader, presumably the Sultan of Ifat at Zeila, while travelling home from Jerusalem, and forcibly circumcised in accordance with Islamic custom before being released back to Ethiopia.