The concept of legitimation is very useful in conceptualising the relationship between religion and worldly authority. Virtually every religion in every society has in some way acted to legitimise (or delegitimise) temporal power. But herein also lies the limitation of the concept. It has been turned into a blanket term that obscures more than it reveals. In what sense exactly does religion assist someone who wants to shore up his or her authority against rivals? If a religious text sanctifies or otherwise elevates a ruler, does this actually help the ruler, or is it merely empty phrasing? How can we ascertain the actual relations of power that lie behind the rhetoric? In order to rethink the notion of legitimation, in this chapter I assess first of all how it is employed in previous studies of Buddhist kingship in East Asia. The mere occurrence of terms like cakravartin in Chinese sources has often sufficed to conclude that Buddhism helped to legitimise temporal rule in China. This is often based on the assumption that there was an ideological program or template that was referred to. While there is indeed a text that may be considered a seminal ‘legitimation text,’ namely the Renwang jing 仁王經[Scripture on the Humane Kings], it is open to many different interpretations and has been appropriated differently in various empires and kingdoms of East Asia. Most often, however, we cannot find any clear source for the why and how of Buddhist legitimation; historical precedent and local cultural and societal factors seem to have played a greater role than scriptural texts. In this chapter, after a critical review of the most important studies in the field, I take a closer look at historical cases to reveal the dominant mechanisms at play. I especially refer to cases from Korean history against the light of findings from Buddhism in Chinese history.