This paper discusses Regiam Maiestatem, known by the mid-fifteenth century to constitute much of Scotland’s ‘ancient law’.Although it was used and cited as an authority of Scotland’s common law into the modern period, Regiam has an unusually controversial past. It is currently understood to have been compiled during the reign of Robert I (1306–29), during Scotland’s ‘wars of independence’ with England, although much of its material is based on the late twelfth-century English legal tractate known as Glanvill. As a result of the relationship between it and Glanvill, Regiam has been both dismissed as constituting ’no part’ of Scots law and as providing evidence for the shared legal framework of Scotland and England. Yet it remains a remarkably understudied work in itself, partly because of its complicated manuscript tradition and its confused and often conflicting readings. This lecture offers a new interpretation of Regiam’s intended purpose by situating it in the context of later thirteenth- and early fourteenth-century political thought and, in so doing, offers a different interpretation of the intellectual underpinnings and practice of Robert I’s kingship.