Religion and the belief in God have made a major comeback. From the fundamentalist turn in predominantly Islamic polities to the spread of Catholicism and Pentecostalism in the global south, and from the increase in religiously devout immigrants in Europe to the rise of the Christian right in the United States, it is hard to overstate the significance of the religious revival in late twentieth and early twenty-first century politics.At the same time, the world has witnessed the rapid spread of constitutionalism and judicial review. Constitutional supremacy—a concept that has long been a major pillar of the American political order—is now shared, in one form or another, by over one hundred and fifty countries and several supra-national entities across the globe.At the intersection of two sweeping global trends—the rise of popular support for principles of theocratic governance, and the spread of constitutionalism and judicial review—a new legal order has emerged: constitutional theocracy.Constitutional theocracy enshrines religion and its interlocutors as “a” or “the” source of legislation, and at the same time adheres to core ideals and practices of modern constitutionalism.Unique hybrids of apparently conflicting commitments, worldviews, and sources of authority, constitutional theocracies thus offer an ideal setting—a “living laboratory” as it were—for studying constitutional law and innovation as a form of politics by other means.In this book, I combine insights from legal theory, economics, theology, and political sociology with a rigorous comparative analysis of religion-and-state jurisprudence from dozens of countries worldwide to explore the evolving role of constitutional law and courts in the emerging non-secularist world.I argue that, counter-intuitively, the constitutional enshrinement of religion may be a rational, prudent strategy that allows opponents of theocratic governance to talk the religious talk without walking most of what they regard as theocracy’s unappealing, costly walk.Many of the jurisdictional, enforcement, and cooptation advantages that gave religious legal regimes an edge in the pre-modern era, are now aiding the modern state and its laws in its effort to contain religion. The “constitutional” in a constitutional theocracy thus fulfils the same restricting function it carries out in a constitutional democracy: it brings theocratic governance under check, and assigns to constitutional law and courts the task of a bulwark against the threat of radical religion.Precisely because it has certain religion-like aspects to it, the canonical constitutional scripture may control and pacify the principles of theocratic governance more effectively than blunter and ostensibly more forceful means. In that respect, I argue, constitutionalism might very well emerge—or perhaps has already emerged—as tomorrow’s “opiate of the masses.”The rise of constitutional theocracy, much like the process of separation of church and state before it, is merely another stage in the ongoing tug-of-war between two of the most powerful belief systems of our time. Constitutional theocracy is a politically driven synthesis that is already becoming the new thesis throughout much of the developing world.Turning to constitutional law and courts to bring religiosity under check or defuse its potentially radical edge is a rational choice of action by secularists and moderates. Despite occasional and inevitable setbacks, it is a prudent, judicious gamble.As de facto civic religion, constitutional scripture may be an effective counterpoint to religious scripture.