Since the 1960s, the concept of civil religion has informed a great number of scholarly works exploring the relationship between religion and nationalism in the west—and beyond. It is therefore not surprising that the concept also informed seminal works on Buddhism and politics in Thailand. In recent years, however, the concept appears to have fallen out of fashion within Thai Studies and perhaps Southeast Asian Studies more broadly. This article surveys and critically discusses the widely diverging and confusing ways in which the concept of civil religion has been used in the study of Thai history and politics. It then seeks to demonstrate the continued relevance and analytical utility of civil religion, understood as a particular kind of nationalism, according to which the state should accommodate or actively encourage and support religious pluralism by developing ideological and institutional links with multiple religious communities. In Thailand the dominant form of civil- religious nationalism is ‘cosmopolitan royalism’, which positions the king as the leading patron and protector of religions (plural). The final section of the paper illustrates how this conception of civil religion might inform both the study of Thai intellectual history and the study of contemporary political contestation.