The history of the Scots language dates from the incursion of Old English into south-eastern Scotland in the 7th century, where it gradually prevailed against Scots Gaelic. The development of Scots as a distinct language was slowed by the incorporation of Scotland into Great Britain in the 17th century, which increased the influence and prestige of English at the expense of Scots. It was also during the 17th century that Scots was introduced to Ireland. Today Scots is spoken by 28% of the population of Scotland and by 2% or 3% of the population of Northern Ireland.

Speakers of Northumbrian Old English settled in south-eastern Scotland in the 7th century, at which time Cumbric was spoken in the south of Scotland up to the Forth-Clyde isthmus, and the possibly related Pictish was spoken further north. At the same time Gaelic speakers began to spread from the Western Coast of Scotland north of the Clyde into the east. Over the next five hundred years with the founding of Scotland and spread of Christianity across the north of Britain by the Columban Church the Gaelic language slowly moved eastwards and southwards across the lowlands. When Northumbrian lands were incorporated into Scotland between the tenth and eleventh centuries, Gaelic became the prestige language there and had some influence, but the south east remained largely English speaking. In the far north, Viking incursions brought Old Norse speakers into Caithness, Orkney, and Shetland.

Scholars of the language generally use the following chronology:

The nature of early forms of the language are obscure due to Viking plundering and destruction, Edward I of England's removal of the national records and their subsequent loss, the destruction of the monasteries in border warfare, and vandalism during the Reformation. It is difficult to assess whether Scots descends largely from the Northumbrian Old English of Lothian or the Anglo-Danish of Yorkshire introduced some four hundred years later, which would explain the Norse elements in Early Scots which are lacking in Northumbrian Old English. According to linguist Paul Johnston, Scots descends "from a radically restructured, Norse-influenced Northumbrian going back to the Danelaw proper as much as from the original dialects of the Bernician settlers." Robert McColl Millar argues that Scots originated as a koiné of the varieties of English spoken in Bernicia and the Danelaw that had been brought to the new burghs.

Northumbrian Old English had been established in south-eastern Scotland as far as the River Forth by the 7th century. It remained largely confined to this area until the 13th century, continuing in common use while Scottish Gaelic was the court language until displaced by Norman French in the early 12th century. English then spread further into Scotland via the burgh.

After the 12th century early northern Middle English began to spread north and eastwards. It was from this dialect that Early Scots, known to its speakers as "English" (Inglis), began to develop, which is why in the late 12th century Adam of Dryburgh described his locality as "in the land of the English in the Kingdom of the Scots" and why the early 13th century author of de Situ Albanie thought that the Firth of Forth "divides the kingdoms of the Scots and of the English".

Most of the evidence suggests that English spread further into Scotland via the burghs, proto-urban institutions which were first established by King David I. Incoming burghers were mainly English (especially from Northumbria and the Earldom of Huntingdon), Flemish and French. Although the military aristocracy employed French and Gaelic, these small urban communities appear to have been using English as something more than a lingua franca by the end of the 13th century. The growth in prestige of English in the 14th century, and the complementary decline of French in Scotland's Royal Court, made English the prestige language of most of eastern Scotland.

Divergence from Northumbrian English was influenced by the Norse of Scandinavian-influenced English-speaking immigrants from the North and Midlands of England during the 12th and 13th centuries, Dutch and Middle Low German through trade and immigration from the low countries, and Romance via ecclesiastical and legal Latin, Norman and later Parisian French due to the Auld Alliance. Some loan words entered the language resulting from contact with Scottish Gaelic, often for geographical features such as ben, glen, crag, loch and strath; however, there are several others like bog from bog (moist or damp), twig (catch on) from tuig (understand), galore (lots of) from gu leòr (plenty), boose or buss from bus (mouth), and whisky from uisge-beatha (water of life).