What's in a name? Constitutions or Regiam?
As stated above, Regiam is now generally agreed to have been compiled probably during the reign of Robert I, after the enactment of several important pieces of statutory legislation in December 1318 at Scone, although how far we can stick to a post-1318 date is something the project is currently looking at. The coinage 'Regiam Maiestatem', however, is only attested from the early fifteenth century (it refers to the first two opening words of the treatise itself). It is referred to as such in 1426, in James I's order to 'amend' the auld lawes of Scotland, which cited by name Regiam Maiestatem and Quoniam Attachiamenta (another legal tractate, compiled in the fourteenth-century). A manuscript dated internally to 1439 actually calls the text 'Regia Majestas'—Royal Majesty. But the earliest version of the text entitle it as either the Constitutiones Regie Regni Scotie ... edite per Dauid Regem that is, the royal constitutions of the kingdom of Scotland, .... published by King David, that is David I, king of Scots (1124-53).
The end of Regiam in the Additional manuscript 18111, fo. 76r.
Inside the Additional manuscript, the work is divided into four parts, although there is some debate about this. Some manuscripts contain a text in three books (this is particularly common in MSS of the first half/middle of the fifteenth century) but this is actually just a repeated scribal error, in which the start of the third book is ignored by a scribe, and later scribes repeated the error. However, even some early four-book manuscripts contain some doubt and error about the work's structure, showing that, whatever the divisions were originally, they were not substantive enough to be copied wholly accurately. A four-part work, however, does seem to be part of the original structure of the work, and is attested in the Additional manuscript.
Earlier generations got quite preoccupied with the issue of whether RM was originally three books or four books. The earliest MS to contain this 'three book RM' is internally dated to 1439 (the same MS as which gives RM its earliest surviving intitulatio). Some manuscripts call these parts books, and give them titles, but the titles are no more than the rubrics of the first chapters of each part. The book 'titles' have given the impression that each book is devoted solely to one particular subject (e.g. book IV de criminalibus); however, this is a mistaken view. The 'parts' themselves contain a yet to be determined order and rationale. There is still much more work to be done to understand the content of Regiam Maiestatem.