The mother of King Bhumibol Adulyadej, Princess Mother Sangwan, was the royal patron of the Thai Border Patrol Police (BPP) and an ardent supporter of its Cold War era civic action programmes. This article surveys the special relationship between the Princess Mother and the BPP and their development of royal projects among the highland minorities in northern Thailand to illuminate the implications of this collaboration for the spread of royalist nationalism and the evolving role of the monarchy from the 1960s to the present.