I Studies in Islamic intellectual history have mostly neglected to systematically investigate the religious beliefs of the practitioners of exact science and the relationship of these beliefs to the broader landscape of theology and philosophy in classical Islam. How do the religious beliefs of natural scientists inform their practice of science, and vice versa? What is the interaction of “science” and “non-science” in their method of inquiry? This dissertation studies these questions by a close reading of the major extant works of the Muslim polymath Abū Rayh&dotbelow;ān al-Bīrūnī (d. ca. 440/1048). It also provides a survey of secondary literature in Bīrūnī studies and a comprehensive outline of his biography. By examining Bīrūnī's engagement with the ideas of Muslim philosophy, theology, and jurisprudence, as well as his approach to the study of nature and the traditions of other nations, it is possible to define the contours of his “method of inquiry.” Although it can be said that an “empirical imperative” functions as a central anchor in Bīrūnī's method—both in the study of nature as well as in the study of culture and tradition—it is an empiricism that knows its limits and leaves room for revelation to operate within its own independent sphere. Bīrūnī's empiricism enables him to challenge the fundamental axioms of Aristotelianism and the metaphysical or dogmatic claims of Muslim philosophers, jurists, and theologians. In Bīrūnī's case, it is exact science that informs and disciplines philosophy and theology, instead of philosophy and theology overreaching and permeating into the exact sciences. His belief in the integrity of the text of the Qur'ān as being of divine origin combined with an empirical imperative and restrained philosophy results in a unique rational theology that is decidedly non-Ash'arī. Regarding the relationship between religion and philosophy/science, similarities of Bīrūnī's method to the approaches of both al-Ghazālī and Ibn Rushd can be observed. These findings raise intriguing possibilities for future studies by including exact scientists into debates that have, thus far, understood to have been primarily between the philosophers and theologians of classical Islam.