This is a presentation of the phonological history of the Scots language.

Scots has its origins in Old English (OE) via early Northern Middle English; though loanwords from Old Norse and Romance sources are common, especially from ecclesiastical and legal Latin, Anglo-Norman and Middle French borrowings. Trade and immigration led to some borrowings from Middle Low German and Middle Dutch. Some vocabulary has also been borrowed from Scotland's other language, Scottish Gaelic.

Consonants

Consonant clusters

Scots preserved OE and word-initially, though this feature is now highly recessive (e.g. knaw 'know', gnegum 'tricky nature').

:OE æmyrġe → Modern Scots emmers 'embers' (compare English

:OE þȳmel → Modern Scots thimmle 'thimble' (compare English )

:OE timber → Modern Scots timmer 'timber'

:French l'ambre → Modern Scots lammer (amber)

:French chambre → Modern Scots chaumer (chamber)

:Anglo-Norman noumbre → Modern Scots nummer (number)

:OE tumbian → Modern Scots tummle (tumble)

Alveolar plosives and were dropped from final (except in some inflected forms like act, expect, strict), , , a

:Latin strictus → Modern Scots strick 'strict'

:Latin corruptus → Modern Scots corrup 'corrupt'

:OE æmtig → Modern Scots empy 'empty'

:OE frēond → Modern Scots freend 'friend'

:OE ald → Modern Scots auld 'old'

Old English became for a number of speakers, though is widespread:

:OE hwæt → Modern Scots whit 'what'

Metathesis occurred in some words.

:OE boga → bowe 'bow'

Similarly, in the Early Scots period, was vocalized after , (becoming and then changing to or , depending on dialect): for example Modern Scots: beard, breid (bread), deid (dead), deif (deaf), heid (head), meat (food), steid (stead) and tread from beard, brēad, dēad, dēaf, hēafod, mete, stede and tredan.

Similarly with Romance words like beast, cheat, conceit, creitur (creature), deceit, ease, please, ream (cream), reison and seison.

Vowel 4

Old English ā became in Early Scots then in Middle Scots and in Modern Scots, for example: aik (oak), ait (oat), braid (broad), gae (go), hale (whole), hame (home), lade (load), mair (more), raip (rope), saip (soap), sair (sore) and nae (no) from āc, āte, brād, gā, hāl, hām, lād, māra, rāp, sāp and nā.

Before , now in Modern central, southern and Ulster varieties and in northern varieties, for example: ane (one), ance (once), bane (bone), gane (gone), nane (none) and stane (stone) from ān, ānes, bān, gān, nān and stān. Similarly with Norse, for example frae (from), kail (cole) and spae (foretell) from frá, kál and spá. The vowel occurs in other words of Norse origin, for example graith (harness), hain (spare) and lair (mud) from greiða, hagna and leir.

Before + consonant, depending on dialect, now or in Modern Scots, for example: airm (arm), airae (arrow), bairn (child), dairn (darn), hairm (harm), hairst (harvest), wairm (warm) and shairp (sharp) from earm, arwe, derne, hearm, hærfest, wearm and sċearp. Similarly with aiple (apple), aix (axe), efter (after), peth (path), and wraith (wrath) from æpel, æx, æfter, pæþ and wræþþu. Similarly with Romance caird (card), cairy (carry), gairden (garden), regaird (regard), mairy (marry), mairtyr (martyr) and pairt (part).

Vowel 5

In open position o became in Early Scots then eventually in Modern Scots, for example: coal, foal, hole and thole endure.

Vowel 6

Old English ū became in Early Scots then in Middle Scots, remaining so but Stem final it became in Southern Scots, for example Modern Scots: brou (brow), broun (brown), cou (cow), dou (dove), doun (down), house (house), hou (how), mou (mouth), mouse (mouse), nou (now), sour (sour) and thoum (thumb) from brū, brūn, cū, dūfe, dūn, hūs, hū, mūþ, mūs, nū, sūr and þūma. Similarly with Norse boun (ready), couer (cower), droup (droop) and stroup (spout), and Romance allou (allow), bouat (lantern), count (count), dout (doubt), pouder (powder) and round (round).

Vowel 6a

Older Scots became vocalised to by the Middle Scots period,