Harar (Amharic: ሐረር; Harari: ሀረር / هَرَرْ‎; Oromo: Adare Biyyo; Somali: Xarar; Arabic: هرر), known historically by the indigenous as Harar-Gey or simply Gey (Harari: ጌይ, ݘٛىيْ, Gēy, lit. 'the city'), is a walled city in eastern Ethiopia. It is also known in Arabic as the City of Saints (Arabic: مدينة الأولياء, romanized: Madīnat al-ʾAwliyāʾ).

Harar is the capital city of the Harari Region. The ancient city is located on a hilltop in the eastern part of the country and is about 500 kilometres (310 mi) from the Ethiopian capital Addis Ababa at an elevation of 1,885 metres (6,184 ft).

For centuries, Harar has been a major commercial center, linked by the trade routes with the rest of Ethiopia, the entire Horn of Africa, the Arabian Peninsula, Asia, and through its ports, the outside world. Harar Jugol, the old walled city, was listed as a World Heritage Site in 2006 by UNESCO in recognition of its cultural heritage. Because of Harar's long history of involvement during times of trade in the Arabian Peninsula, the Government of Ethiopia has made it a criminal offence to demolish or interfere with any historical sites or fixtures in the city. These include stone homes, museums and items discarded from war. According to UNESCO, it is "considered 'the fourth holiest city' of Islam" with 82 mosques, three of which date from the 10th century, and 102 shrines.

Yahyá Naṣrallāh's Fatḥ Madīnat Harar, an unpublished history of the city in the 13th century, records that the legendary saint Abadir Umar ar-Rida and several other religious leaders settled in the Harar plateau c. 1216 (612 AH). Harar was later made the new capital of the Adal Sultanate in 1520 by the Sultan Abu Bakr ibn Muhammad. The city saw a political decline during the ensuing Emirate of Harar, only regaining some significance in the Khedivate of Egypt period. During the Ethiopian Empire, the city decayed while maintaining a certain cultural prestige.

The etymology of the name "Harar" remains ambiguous; however, archaeologist Timothy Insoll suggests that it may be derived from Harla, an ancient group that existed prior to the arrival of the Oromo people in the area. Other possible etymologies include ones put forth by British explorer Richard Francis Burton who states Harar is an extract of the name of a plain located south of the town or a specific tree.

Harar and its residents were also historically known as Hadharee by outsiders in the region. In the Arabic language, hadhariy serves as both the noun and the adjective that refers to an urban inhabitant and everything associated with a permanent settlement.

When Harar was founded is unclear and various dates have been suggested, some state the city was founded by Qurayshi settlers in the late 7th century or a local creation in the 10th century. Islam had gained a foothold on the Harar plateau by the 10th–11th centuries CE via trade with Zeila. By the 13th century, Islam had become the predominant religion in the region.

It is likely the original inhabitants of the region were the Harla people. Harar was part of the Harla Kingdom's domain in the sixth century. In the Islamic period, the city was under an alliance called the confederated states of Zeila. According to the 12th-century Jewish traveler Benjamin of Tudela, the Zeila was the land of the Havilah, confined by al-Habash in the west. In the ninth century, Harar was under the Maḥzūmī dynasty's Sultanate of Shewa.