The House of Stuart, originally spelt Stewart, also known as the Stuart dynasty, was a royal house of Scotland, England, Ireland and later Great Britain. The family name comes from the office of High Steward of Scotland, which had been held by the family progenitor Walter fitz Alan (c. 1150). The name Stewart and variations had become established as a family name by the time of his grandson Walter Stewart. The first monarch of the Stewart line was Robert II; he and his descendants were monarchs of Scotland from 1371 and of England, Ireland and Great Britain from 1603, until 1714. Mary, Queen of Scots (r. 1542–1567), was brought up in France where she adopted the French spelling of the name Stuart.

In 1503, James IV married Margaret Tudor, thus linking the reigning royal houses of Scotland and England. Margaret's niece, Elizabeth I of England died without issue in 1603, and James IV's and Margaret's great-grandson James VI of Scotland acceded to the thrones of England and Ireland as James I in the Union of the Crowns. The Stuarts were monarchs of Britain and Ireland and its growing empire until the death of Queen Anne in 1714, except for the period of the Commonwealth between 1649 and 1660.

In total, nine Stewart/Stuart monarchs ruled Scotland alone from 1371 until 1603, the last of whom was James VI, before his accession in England. Two Stuart queens ruled the isles following the Glorious Revolution in 1688: Mary II and Anne. Both were the Protestant daughters of James VII and II by his first wife Anne Hyde and the great-grandchildren of James VI and I. Their father had converted to Catholicism and his new wife gave birth to a son in 1688, who was to be brought up as a Roman Catholic; so James was deposed by Parliament in 1689, in favour of his daughters. However, neither daughter had any children who survived to adulthood, so the crown passed to the House of Hanover on the death of Queen Anne in 1714 under the terms of the Act of Settlement 1701 and the Act of Security 1704. The House of Hanover had become linked to the House of Stuart through the line of Elizabeth Stuart, Queen of Bohemia.

After the loss of the throne, the descendants of James VII and II continued for several generations to attempt to reclaim the Scottish and English (and later British) throne as the rightful heirs, their supporters being known as Jacobites. Since the early 19th century, when the James II direct line failed, there have been no active claimants from the Stuart family. The current Jacobite heir to the claims of the historical Stuart monarchs is a distant cousin Franz, Duke of Bavaria, of the House of Wittelsbach. The senior living member of the royal Stewart family, descended in a legitimate male line from Robert II of Scotland, is Andrew Richard Charles Stuart, 9th Earl Castle Stewart.

The ancestral origins of the Stuart family are obscure—their probable ancestry is traced back to Alan fitz Flaad, a Breton who went to England not long after the Norman Conquest. Alan had been the hereditary steward of the Bishop of Dol in the Duchy of Brittany; Alan had a good relationship with Henry I of England who awarded him with lands in Shropshire. The FitzAlan family quickly established themselves as a prominent Anglo-Norman noble house, with some of its members serving as high sheriffs of Shropshire. It was the son of Alan named Walter FitzAlan who became the first hereditary high steward of Scotland, while his brother William's family went on to become earls of Arundel.

When the civil war in the Kingdom of England, known as The Anarchy, broke out between Empress Matilda and King Stephen, Walter had sided with Matilda. Another supporter of Matilda was her uncle David I of Scotland from the House of Dunkeld. After Matilda was pushed out of England into the County of Anjou, essentially failing in her attempt for the throne, many of her supporters in England fled also. It was then that Walter followed David up to the Kingdom of Scotland, where he was granted lands in Renfrewshire and the title for life of lord high steward. The next monarch of Scotland, Malcolm IV, made the high steward title a hereditary arrangement. While high stewards, the family were based at Dundonald, South Ayrshire, between the 12th and 13th centuries.

The sixth high steward of Scotland, Walter Stewart (1293–1326), married Marjorie, daughter of Robert the Bruce, and also played an important part in the Battle of Bannockburn gaining further favour. Their son Robert was heir to the House of Bruce, the Lordship of Cunningham and the Bruce lands of Bourtreehill; he eventually inherited the Scottish throne when his uncle David II died childless in 1371.

In 1503, James IV attempted to secure peace with England by marrying King Henry VII's daughter, Margaret Tudor. The birth of their son, later James V, brought the House of Stewart into the line of descent of the House of Tudor, and the English throne. Margaret Tudor later married Archibald Douglas, 6th Earl of Angus, and their daughter, Margaret Douglas, was the mother of Henry Stuart, Lord Darnley. In 1565, Darnley married his half-cousin Mary, Queen of Scots, the daughter of James V. Darnley's father was Matthew Stewart, 4th Earl of Lennox, a member of the Stewart of Darnley branch of the House. Lennox was a descendant of Alexander Stewart, 4th High Steward of Scotland, also descended from James II, being Mary's heir presumptive. Thus Darnley was also related to Mary on his father's side and because of this connection, Mary's heirs remained part of the House of Stuart. Following John Stewart of Darnley's ennoblement for his part at the Battle of Baugé in 1421 and the grant of lands to him at Aubigny and Concressault, the Darnley Stewarts' surname was gallicised to Stuart.