After the Safavid Empire collapsed in 1722, countless Shi‘i families dispersed from the capital of Isfahan, moving to “Shi‘i” towns in Iraq, Iran, India, and elsewhere. Shi‘i strongholds and the networks that connected them, therefore, crisscrossed national and ethnic “boundaries.” The movement of neo-Usulism, which has been the dominant school of thought in Twelver Shi‘ism since the late eighteenth century, exemplifies the transnational character of modern Shi‘ism. The neo-Usuli movement was founded in southern Iraq by Arab and Persian scholars, some of whom were recent immigrants from Safavid Iran. These scholars cultivated scholarly and financial relationships with Shi‘is in Iraq, Iran, and India, and developed the cities of Najaf and Karbala’ as the preeminent centers of pilgrimage and scholarship for the international Shi‘i community. By the mid-nineteenth century, Qajar rule in Iran attracted some Usuli scholars back to Iran. Although these scholars established or re-established Shi‘i centers of learning in Isfahan and other Iranian cities, the nucleus of the Shi‘i world remained in Najaf. Shi‘i scholars in Iraq influenced Iranian politics from outside its national borders. Additionally, transnational patron-client relationships allowed Shi‘i scholars in Iran and Iraq to maintain their political independence from the Qajars (and Ottomans). The rise of the Shi‘i seminary complex in Qum in the mid-twentieth century bifurcated Arab and Iranian Shi‘ism, which illustrates the increased nationalization, decentralization, and ethnicization of Shi‘ism. My research makes use of Shi‘i biographical dictionaries, the scholarly writings of neo-Usuli scholars, and family histories of the Bihbihani, Bahr al-‘Ulum, and Tabataba’i clerical dynasties. I argue that modern Shi‘ism, illustrated by neo-Usulism, emerged as a transnational movement, primarily connecting southern Iraq and Iran. This is in contradistinction to Islamic movements of the twentieth century that were forged in the context of nationalism and nation-state building. My argument that neo-Usulism is a modern transnational movement challenges the hypothesis put forward by the doyen of world-systems theory, Emmanuel Wallerstein, which suggests that modern social movements are reactions to capitalism, most of which are nationalist, socialist, or both. I contend that Wallerstein’s argument ignores modern religious movements, including neo-Usulism, which was neither socialist nor nationalist. Although Shi‘i clerics have certainly been influenced by the nationalization of the Shi‘i world, they are not bound by their national communities. Prominent Arab and Iranian Ayatollahs, therefore, continue to function in a multiplicity of transnational contexts, as illustrated by their multi-lingual websites and multinational economic ventures.