The most well-known elements of Montesquieu’s political thought are his liberal constitutionalism and his emphasis on the need for a fit between a regime and a populace. But scholars have rarely sought to understand the theoretical relationship between these elements, and some have denied that they are meaningfully related at all. I argue that Montesquieu’s liberal constitutionalism and his political particularism are theoretically harmonious and mutually reinforcing elements of a unified project. Montesquieu’s liberal political philosophy possesses in-built sources of resistance to the rationalistic and universalistic political projects often associated with modern liberalism.