The Isaaq (Somali: Reer Sheekh Isxaaq) is a major Somali clan. It is one of the largest Somali clan families in the Horn of Africa, with a large and densely populated traditional territory. The Isaaq people claim in a traditional legend to have descended from Sheikh Ishaaq bin Ahmed, an Islamic scholar who purportedly traveled to Somaliland in the 12th or 13th century and married two women; one from the local Dir clan. He is said to have sired eight sons who are the common ancestors of the clans of the Isaaq clan-family. He remained in Maydh until his death.

Somali genealogical tradition places the origin of the Isaaq tribe in the 12th or 13th century with the arrival of the Sheikh Ishaaq Bin Ahmed (Sheikh Ishaaq) from Arabia. Sheikh Ishaaq settled in the coastal town of Maydh in modern-day northeastern Somaliland. Hence, Sheikh Ishaaq married two local women in Somaliland, which left him with eight.

There are also numerous existing hagiographies in Arabic which describe Sheikh Ishaaq's travels, works and overall life in modern Somaliland, as well as his movements in Arabia before his arrival. Besides historical sources, one of the more recent printed biographies of Sheikh Ishaaq is the Amjaad of Sheikh Husseen bin Ahmed Darwiish al-Isaaqi as-Soomaali, which was printed in Aden in 1955.

Sheikh Ishaaq's tomb is in Maydh, and is the scene of frequent pilgrimages. Sheikh Ishaaq's mawlid (birthday) is also celebrated every Thursday with a public reading of his manaaqib (a collection of glorious deeds). His Siyaara or pilgrimage is performed annually both within Somaliland and in the diaspora particularly in the Middle East among Isaaq expatriates.

The dialect of the Somali language that the Isaaq speak has the highest prestige of any other Somali dialect.

The Isaaq are estimated to number 3-4 million according to a 2015 estimate, and roughly comprise around 22% of all Somalis.

The Isaaq have a very wide and densely populated traditional territory and make up 80% of Somaliland's population, and live in all of its six regions (Awdal, Marodi Jeh, Togdheer, Sahil, Sanaag and Sool). The Isaaq have large settlements in the Somali Region of Ethiopia, mainly on the eastern side of Somali Region also known as the Hawd and formerly Reserve Area which is mainly inhabited by the Isaaq residents. A subclan of the Habr Yunis, the Damal Muse (also known as the Dir Rooble), also inhabit the Mudug region of Somalia. The Habarnoosa, a clan of the Hadiya people in the Hadiya Zone claim descent from the Habr Yunis subclan of Isaaq. The Isaaqs also have large settlements in Naivasha, Kenya, where the Ishaakia make up a large percentage of the Kenyan population, and in Djibouti, where the Isaaq account for 20% of Djibouti's population.

The Isaaq tribe are the largest group in Somaliland. The populations of five largest cities in Somaliland – Hargeisa, Burao, Berbera, Erigavo and Gabiley – are all predominantly Isaaq and historically native to Zeila. They exclusively dominate the Marodi Jeh region, and the Togdheer region, and form a majority of the population inhabiting the western and central areas of Sanaag region, including the regional capital Erigavo. The Isaaq also have a large presence in the western and northern parts of Sool region as well, with Habr Je'lo sub-clan of Isaaq living in the Aynabo district whilst the Habr Yunis subclan of Garhajis lives in the eastern part of Xudun district and the very western part of Las Anod district. They also live in the northeast of the Awdal region, with Saad Muse sub-clan being centered around Lughaya and its environs. The Arap live Somalia Bakool Rabdhure District the live also Fafan Zone and Baligubadle.^{[citation needed]}