Thailand in the late 19th and early 20th centuries transformed its legal and administrative structure from one based on the principles of sacred kingship to one based on the symbols of a constitutional monarchy in a Western-style nation-state. This transformation had important implications for the status of the Muslim minority population residing primarily in the four southernmost provinces of Thailand. Traditionally, one of the most important responsibilities of the Thai king was to uphold and protect Thai Buddhism and to oversee and purify the Buddhist clergy. In the new nation-state, these governmental responsibilities were generalized to some extent to include other religions of Thai citizens, such as Islam. This process of generalization, however, was associated with certain conceptual and political problems, whose analysis in this article sheds light not only on the status of the Muslim minority in contemporary Thailand but also on modern concepts of religion, law, and kingship in the Thai polity.