The Ulster Scots are an ethnic group that has lived on the island of Ireland since the 17th Century, and are predominantly citizens of the United Kingdom.

Their ancestors are Scots from the Scottish Lowlands and English people from counties close to Scotland, many being from the "Border Reivers" culture.

These people migrate to the island of Ireland in large numbers with the Plantation of Ulster, a planned process of colonization that takes place under the auspices of James VI of Scotland and I of England on land often confiscated from the Irish nobility, most extensively in the Province of Ulster.

The term "Ulster-Scots" refers to both these colonists of the 17th century and, less commonly, to the Gallowglass who began to arrive from what is now northwest Scotland centuries earlier.Ulster-Scots are largely descended from colonists from Galloway, Ayrshire, and the Scottish Borders Country, although some descend from people further north in the Scottish Lowlands and the Highlands.

Ulster-Scots emigrate in significant numbers to the United States and all corners of the then-worldwide British Empire — Canada, Australia, New Zealand, South Africa — and to a lesser extent to Argentina and Chile in South America.

Scotch-Irish is a traditional term for Ulster Scots who later emigrate to what is now the United States; "Scots-Irish" is a more recent form of the American term, and is not to be confused with Irish-Scots, i.e., recent Irish immigrants to Scotland.