Primitive Irish is known only from fragments, mostly personal names, inscribed on stone in the Ogham alphabet in Ireland and western Britain up to about the 6th century AD.

There are a large number of borrowings from Latin, (muinntir, Didòmhnaich), ancient Greek, especially in the religious domain (eaglais, Bìoball from ἐκκλησία ekklesia and βίβλος biblos), Norse (eilean, sgeir), Hebrew (Sàbaid, Aba), French (seòmar) and Scots (aidh, bramar).

In common with other Indo-European languages, the neologisms which are coined for modern concepts are typically based on Greek or Latin, although written in Gaelic orthography; "television", for instance, becomes telebhisean and "computer" becomes coimpiùtar.

The influence of Scottish Gaelic can be seen particularly in surnames (notably Mac- names, where the mac means "Son of...") and toponymy.

The surname influence is not restricted to Mac- names: several colours give rise to common Scottish surnames: bàn (Bain – white), ruadh (Roy – red), dubh (Dow – black), donn (Dunn – brown), buidhe (Bowie – yellow), and Gille- (meaning lad or servant) gives rise to names such as Gilmour and Gillies.

The ancestral Common Brittonic language was probably spoken in southern Scotland in Roman times and earlier.

[5] It was certainly spoken there by the early medieval era, and Brittonic-speaking kingdoms such as Strathclyde, Rheged, and Gododdin, part of the Hen Ogledd ("Old North"), emerged in what is now Scotland.

At its height, it may have been spoken from Shetland down to Fife, but it was pushed back as Scots and Anglo-Saxons invaded Northern Britain, each with their own language.

That began to diverge from the Northumbrian variety due to 12th and 13th century immigration of Scandinavian-influenced Middle English-speakers from the North and Midlands of England.

[7]: xliii  Later influences on the development of Scots were from Romance languages via ecclesiastical and legal Latin, Norman[7]: lxiii–lxv  and later Parisian French due to the Auld Alliance; as well as Dutch and Middle Low German influences due to trade and immigration from the Low Countries.

[7]: lxi  Contemporary Scottish Gaelic loanwords are mainly for geographical and cultural features, such as ceilidh, loch and clan, and also occur in colloquialisms such as gob and jilt.

By the 16th century Middle Scots had established orthographic and literary norms largely independent of those developing in England.

This variety abandoned some of the more distinctive old Scots spellings,[9] adopted many standard English spellings (although from the rhymes it is clear that a Scots pronunciation was intended)[10]: xv  and introduced what came to be known as the apologetic apostrophe,[10]: xiv  generally occurring where a consonant exists in the Standard English cognate.

This Written Scots drew not only on the vernacular but also on the King James Bible, and was also heavily influenced by the norms and conventions of Augustan English poetry.

[11] Consequently, this written Scots looked very similar to contemporary Standard English, suggesting a somewhat modified version of that, rather than a distinct speech form with a phonological system which had been developing independently for many centuries.

Commenting on this, John Corbett (2003: 260) writes that "devising a normative orthography for Scots has been one of the greatest linguistic hobbies of the past century".

Norn evolved from the Old Norse that was widely spoken in the Hebrides, Orkney, Shetland and the west coast of the mainland during the Viking occupation from the 8th to the 13th centuries.

In Foula, on the other hand, men who were living very much later than the middle of the present [19th] century are said to have been able to speak Norn[16]Most of the use of Norn/Norse in modern-day Shetland and Orkney is purely ceremonial, and mostly in Old Norse, for example the Shetland motto, which is Með lögum skal land byggja ("with law shall land be built"), which is the same motto used by the Icelandic police force and inspired by the Danish Codex Holmiensis.

These developments were offset by the acquisition of the Norse-Gaelic west, and the Gaelicisation of many of the noble families of French and Anglo-French origin and national cohesion was fostered with the creation of various unique religious and cultural practices.

By the end of the period, Scotland experienced a "Gaelic revival" which created an integrated Scottish national identity.

There are no universally accepted criteria for distinguishing languages from dialects, although a number of paradigms exist, which render sometimes contradictory results.

Since there is a very high level of mutual intelligibility between contemporary speakers of Scots in Scotland and in Ulster (Ulster Scots dialect), and a common written form was current well into the 20th century, the two varieties have usually been considered as dialects of a single tongue rather than languages in their own right; the written forms have diverged in the 21st century.

Two areas with mostly Norse-derived placenames (and some Pictish), the Northern Isles (Shetland and Orkney) were ceded to Scotland in lieu of an unpaid dowry in 1472, and never spoke Gaelic; its traditional vernacular Norn, a derivative of Old Norse mutually intelligible with Icelandic and Faroese, died out in the 18th century after large-scale immigration by Lowland Scots speakers.