The Ulster-Scots language is a regional variant of Scots, which is itself a Germanic language that developed from the Northumbrian dialect of Anglo-Saxon towards the end of the first millenium AD. The English language developed during the same period from more southerly forms of Anglo-Saxon speech – chiefly those of Mercia and Wessex. Scots and English are therefore closely related, although they employ some different vocabulary and grammar as well as pronunciation.

The Scots language was introduced into Ulster during the population movements that followed the union of the Scottish and English crowns, the breaking of the border, and the various plantations of Protestant settlers into Ulster that took place during the early 17th Century. Within Ulster it developed a distinctive form influenced both by the English which was the official language of Ireland at the time, and the Scots and Irish Gaelic speech communities with which it was in close contact.

The tradition of written Ulster-Scots can be traced back 400 years in letters, historical documents and church records. The most significant literature in Ulster-Scots is probably that produced by the 18th Century Weaver poets, who were strongly influenced by the Ayrshire poet, Rabbie Burns.

It has been questioned whether Ulster-Scots can really be distinguished from Ulster-English dialect. Historically, Ulster-Scots, like other variants of Scots, was denigrated as simply ‘bad English’. Prof. Michael Montgomery has noted 67 marker words by which Ulster-Scots may be distinguished from Standard English. Only 22 of these marker words are also present in Ulster-English dialect (Ulster-Scots Agency leaflet -What is Ulster-Scots?). There is, therefore, a real difference, but drawing sharp lines between the two is difficult as the two forms of speech have always been in constant interaction, and Ulster-Scots speakers habitually speak Ulster-English dialect to those outside their own language community.

A similar controversy has surrounded Norn, the Scandinavian influenced speech of Caithness and the Northern Isles. Whilst northern communities define it as a language, others, particularly in Edinburgh, have claimed that it is simply a dialect of Scots. It is notable that in this case, however, nobody has suggested that it is a dialect of English.

Montgomery notes that the relationship between English and Ulster-Scots "is similar to that often found in continental Europe, where national and regional languages share a history (for example, Catalan and Spanish or Frisian and Dutch).

It used to be said that a language was a dialect with an army. In today’s Europe perhaps it could be said that a language is a dialect with EU recognition. In either case it is clear that whose speech is defined as a language and whose as a dialect depends very much on the power of those doing the defining. Ulster-Scots was recognised officially as a European regional language in 1992, part of a general trend in Europe to look away from the old centres of power and for an increased valuation of regional languages and cultures. The Ulster-Scots language is promoted within the province by the Ulster-Scots Language Society, the Ulster-Scots Agency and the Ulster-Scots Heritage Council.

Perhaps the final word on the subject may go to Willie Drennan, who comments that "It doesn’t matter whether you call it a language or a dialect, what matters is that it is a different way of speaking and a different way of thinking, and as such, it is worth holding on to". The Ulster-Scots Folk Orchestra use both the Ulster-Scots language and Ulster-English dialect in their performances.