One of the fascinating but seldom-explored phenomena in comparative constitutional law is the growing reliance on constitutional courts in the non-secular world to block the spread of religiosity or advance a relatively universalist interpretation of sacred texts. The American constitutional system has successfully maintained a stable secular order in one of the most religious societies in the West. Although the specter of religiosity is haunting Europe once again, European national high courts, from Germany to Britain to France, assumed the role of guardians of secularism against the perceived threat to the concept of a religiously neutral public sphere. Likewise, Turkey's adherence to a strict separation of religion and state (at least until the recent constitutional amendments) has allowed the Turkish Constitutional Court to exclude religious practices, parties, and policies from the purview of Turkey's political sphere. The Supreme Court of India has drawn on the “basic structure” doctrine to maintain and advocate a secularist vision of the Indian Constitution amid a markedly religious setting and increased political presence of Hindu and Muslim religiosity. Its jurisprudence on personal-status law has sounded a clear voice for uniformity and standardization in that domain. In short, despite the many pertinent differences, the constitutional jurisprudence of countries that adhere to a strict separation of religion and state reveals a clear secularist tendency and vision of religion as confined to the private sphere.

A notably harder challenge to the constitutional containment of religion is posed by constitutional orders that defy the Franco-American ideal of separating religion and state along private-public lines. At least 1 billion people now live in polities or subnational units that not only designate a single religion as the “state religion” but also enshrine that religion and its interlocutor as “a” or “the” source of legislation (meaning that legislation must comply with principles of that religion), incorporate religious precepts in law, grant religious tribunals jurisdiction over important aspects of life, public and private, in addition to the tremendous symbolic weight religious edicts often carry. At the same time, religion and its institutions and interpretive hierarchy are expected to comply with overarching constitutional norms and are subject to review by constitutional courts and judges.