This dissertation is a study of the early 20th-century Pan-Islamist reform movement in Bosnia-Herzegovina, tracing its origins and trans-imperial development with a focus on the years 1901-1914. Its central figure is the theologian and print entrepreneur Mehmed Džemaludin Čaušević (1870-1938), who returned to his Austro-Hungarian-occupied home province from extended studies in the Ottoman lands at the start of this period with an ambitious agenda of communal reform. Čaušević’s project centered on tying his native land and its Muslim inhabitants to the wider “Islamic World”—a novel geo-cultural construct he portrayed as a viable model for communal modernization. Over the subsequent decade, he and his followers founded a printing press, standardized the writing of Bosnian in a modified Arabic script, organized the country’s Ulema, and linked these initiatives together in a string of successful Arabic-script, Ulema-led, and theologically modernist print publications. By 1914, Čaušević’s supporters even brought him to a position of institutional power as Bosnia-Herzegovina’s Reis-ul-Ulema (A: raʾīs al-ʿulamāʾ), the country’s highest Islamic religious authority and a figure of regional influence between two empires. Methodologically, the project functions on two primary levels. The first is a close reading of the reform movement’s multilingual and multi-scriptural periodical press and publishing scene, situating this fin-de-siècle Muslim print culture in its late imperial and trans-regional context. The second is a prosopographical approach to the polyglot generation of writers and theologians who stood behind it, emphasizing networks of collaboration, education, and kinship that tied them both to the wider world and previous generations of Bosnian scholars. The dissertation ultimately argues that Čaušević and his movement emerged from and represented a locally grounded tradition of Muslim cosmopolitan reform, which insisted on religious instruction in the Bosnian vernacular not at the expense of the classical languages of higher Islamic learning or the Ottoman (and later Habsburg) imperial order, but rather as a foundation that would enable Muslims to pursue the former and buttress the latter as well. In making this case, the project contributes to the wider historiography on empires and nationalism in Eastern and Southeast Europe, reconsidering the role of multilingualism in imperial demise and moving beyond the prevailing top-down focus on Muslims and other ethno-religious minorities as beleaguered subjects of nationalizing states. At the same time, it serves as a Bosnian case study for outstanding concerns in global Islamic intellectual history, arguing that the late and post-Ottoman Balkans played an active and underappreciated role in the formation of transnational Pan-Islamist thought during the late imperial period.