Clan Macdonald of Sleat, sometimes known as Clan Donald North and in Gaelic Clann Ùisdein [kʰl̪ˠan̪ˠ ˈuːʃtʲɛɲ], is a Scottish clan and a branch of Clan Donald—one of the largest Scottish clans. The founder of the Macdonalds of Sleat was Ùisdean, or Hugh, a 6th great-grandson of Somerled, a 12th-century Lord of the Isles (Rì Innse Gall). The clan is known in Gaelic as Clann Ùisdein ("children of Ùisdean"), and its chief's Gaelic designation is Mac Ùisdein ("son of Ùisdean"), in reference to the clan's founder. Both the clan and its clan chief are recognised by the Lord Lyon King of Arms, who is the heraldic authority in Scotland.

The Macdonalds of Sleat participated in several feuds with neighbouring clans, most notably the Macleods of Harris & Dunvegan and the Macleans of Duart. The clan also suffered from infighting in the early 16th century, as the leading members of the clan fought and murdered each other.

The clan seems to have grudgingly supported the Royalist cause in the Wars of the Three Kingdoms, and suffered grievously in military defeats against Parliamentarian forces. The clan supported the Jacobite cause in the 1715 rebellion, yet refused to come out for Bonnie Prince Charlie and his father a generation later in 1745. In the early 18th century, the clan's chief was involved in a plan to sell tenants into indentured servitude in the American Colonies. By the late 18th century, the chiefs had alienated themselves from the common clansfolk, when they seated themselves in northern England and rarely visited the old clan lands. The 18th and 19th centuries witnessed the suffering of the common clansfolk, as many were cleared off their lands at the hands of their absentee landlords. Today members and descendants of the clan live all over the world.

Much of the history of the Macdonalds of Sleat comes from traditional family histories, and it is often difficult, if not impossible, to tell fact from fiction. The clan histories relevant to the Macdonalds of Sleat were composed by the shanachies (historians or story tellers) MacVuirich – the Clanranald shenachie – and Hugh Macdonald – the Sleat shenachie. Contemporary records that shed light upon the early history of the clan include charters and confirmations of charters granted by kings, and various bonds of manrent entered with other landlords and clan chiefs.

The Macdonalds of Sleat are a branch of Clan Donald — one of the largest Scottish clans. The eponymous ancestor of Clan Donald is Domhnall, son of Raghnall, son of Somhairle. Traditional Clan Donald genealogies, created in the Late Middle Ages, give the clan a descent from various legendary Irish figures. Modern historians, however, distrust these traditional genealogies, and consider Somhairle, son of Gille Brighde to be earliest ancestor for whom there is secure historical evidence. Somhairle, himself, was a 12th-century leader, styled "king of the isles" and "king of Argyll"; yet there is no reliable account for his rise to power.

The Macdonalds of Sleat descend from Domhnall's son, Aonghas Mór; and then from his son, Aonghas Óg. Angus Óg's son, Eoin, was the first to officially claim the title Lord of the Isles, though many Macdonalds before him had the position. Eoin I's first marriage was to Áine, heiress of Clann Ruaidhrí (which was founded by Ruaidhrí, elder brother to Domhnall, founder of Clan Donald). Eoin I later divorced Áine and married Margaret, daughter of Robert II. The children from Eoin I's first marriage were then passed over in the main succession of the chiefship of Clan Donald and later Macdonald lords of the isles, in favour of those from his second marriage. Eoin I was succeeded by his son, Domhnall of Islay; who was in turn succeeded by his son, Alasdair of Islay. The Macdonalds of Sleat descend from Ùisdean, son of Alasdair of Islay, Lord of the Isles, and the daughter of Ó Beólláin (O'Beolan), lay Abbot of Applecross. Hugh was born in the first quarter of the 15th century and his father, Alexander, Lord of the Isles and later Earl of Ross, gave him the Sleat lands on the Isle of Skye. The Macdonalds of Sleat are also known in Gaelic as Clann Ùisdein ("the children of Ùisdein").

The first record of Ùisdean occur in the traditional histories of the shenachie MacVurich and Hugh Macdonald. According to the Sleat shenachie, Ùisdean, along with several young men from the Western Isles went on a raiding expedition to Orkney. The tradition runs that the Western Islesmen were victorious in their conflict with the Northern Islesmen, and that the Earl of Orkney was also slain. Ùisdean is then said to have ravaged Orkney, and carried off much loot. According to Angus and Archibald Macdonald, Ùisdean's expedition took place around 1460, when he did not appear to hold title to any of the lands his family would come to hold. In fact, in the year 1463, Eoin II, Lord of the Isles granted Ùisdean's older brother, Celestine, the 28 merklands of Sleat, in addition to extensive lands in west Ross given to him by their father, Alexander, Lord of the Isles and Earl of Ross in the early 15th century.

In 1469, Ùisdean received from the Earl of Ross the 30 merklands of Skeirhough in South Uist; the 12 merklands of Benbecula, and the merkland of Gergryminis also in Benbecula; the 2 merklands of Scolpig, the 4 merklands of Tallowmartin, the 6 merklands of Orinsay, the half merkland of Wanlis, all in North Uist; and also confirmed him in the 28 merklands of Sleat. The earliest Clann Ùisdein seat connected with the barony of Sleat was Dunscaith Castle, off the Sound of Sleat. Ùisdean played not a small part in securing the surrender of the Earl of Ross, for which he was promised by the king 20 pounds worth of land, in 1476. The lordship of the isles was forfeited in 1493 due to the actions of John of Islay, Earl of Ross, Ùisdean's older brother. Ùisdean obtained a royal confirmation for his lands granted to him by the Earl of Ross in 1469. Ùisdean died in 1498, and was buried at Sand, in North Uist.