Clan MacDougall is a Scottish clan traditionally associated with the lands of Argyll and Lorne in Scotland. Like the Clan Donald or MacDonald and all of its MacDonald branches, the MacDougalls are also descended from Somerled ("Summer Wanderer"), also known as Lord of the Isles. Together they are referred to as the Clann Somhairle. Furthermore they are descended maternally from both the House of Godred Crovan and the Earls of Orkney, through Somerled's wife Ragnhildis Ólafsdóttir, daughter of Olaf I Godredsson, King of Mann and the Isles and Ingeborg Haakonsdottir daughter of Haakon Paulsson, Earl of Orkney. It remains uncertain if the Clann Somhairle are also descendants in some manner of the House of Ivar, but this is commonly argued.

The Clan MacDougall takes its name from Dubgall mac Somairle, the eldest son of Somerled by Ragnhild, who, after his father's death in 1164, held most of Argyll and also islands such as the Isle of Mull, Lismore, Jura, Tiree, Coll, Iona and many others.

The names Dougall or Dugald are derived from the Gaelic dubh-gall, meaning "dark stranger", as distinct from the 'fionn-gall', to which the Dòmhnullaich of the Rìoghach Innse Gall were associated. Dougall's royal descent was acknowledged by the king of Norway. His son, Duncan, and his grandson, Ewan, built castles to defend their dominions, including Dunstaffnage, Dunollie and Duntrune on the mainland, and Aros, Cairnburgh, Dunchonnel and Coeffin on the islands. Dunollie, a craig rising up over seventy feet, was most likely fortified as early as the sixth century and was to become the chief seat. Duncan also built Ardchattan Priory, where the MacDougall chiefs were buried until 1737.

After Haakon IV of Norway had been defeated by the Scottish army at the Battle of Largs in 1263 the Clan MacDougall attacked his fleet. The Norsemen were defeated by the MacDougalls in the sea battle.

The MacDougalls were mortal enemies of the Clan Campbell and defeated them at the Battle of Red Ford in 1296, led by their chief Alexander MacDougall of Argyll.