This study provides a comprehensive examination of the evolution of Islam as a ruling framework in postrevolutionary Iran up to the present day. Beginning with the position and structure of Iran's clerical establishment under the Islamic Republic, Kamrava delves into the jurisprudential debates that have shaped the country's political institutions and state policies. Kamrava draws on extensive fieldwork to examine various religious narratives that inform the basis of contemporary Iranian politics, also revealing the political salience of common practices and beliefs such as religious guardianship and guidance, Islam as a source of social protection, the relationship between Islam and democracy, the sources of divine and popular legitimacy, and the theoretical justifications for religious authoritarianism. Providing access to many Persian-language sources for the first time, Kamrava shows how religious intellectual production in Iran has impacted the ongoing transformation of Iranian Shi'ism, and ultimately underwritten the fate of the Islamic Republic.