Survey of the activities of one of the most important cross-Border families, the ancestors of Robert the Bruce.Robert de Brus, the conquisitor of Cleveland, Hartness and Annandale, who came into England among the followers of Henry I, was also a close companion and mentor of David I, king of Scots. The lands he acquired from bothkings were divided between his sons, from whom two lines descended: the lords of Skelton, influential Northerners who played an active part during the baronial troubles in the reigns of John and Henry III, and the prominent cross-Border lords of Annandale, co-heirs of the substantial Chester and Huntingdon estates and progenitors of King Robert Bruce. This study takes a fresh approach to the Brus family by assessing the achievements of the two lines in parallel while examining the extent of their power and the development of their lordships; it highlights the inter-relations between the barons of England and Scotland during two hundred years of comparative peace between the kingdoms. Of additional interest is the appendix of an extensive handlist of charters of the Brus family of both lines. It will be a welcome addition to the existing body of works on English baronial families and on Anglo-Scottish cross-Border lords of the twelfth and thirteenth centuries.