This dissertation addresses the scientific practice and science education of the members of the Society of Jesus in the early modern period. Drawing on the career of the Jesuit mathematician and instructor at the Collegio romano, Orazio Grassi, this study examines not only the scientific content in his normative publications, but also includes the content related to his students in the classroom in the early seventeenth century. In doing so, this study provides a record of scientific education in mathematics at the Collegio romano during the early seventeenth century. Far from the popular narratives espoused by histories of science of the twentieth century, in which the Society of Jesus was depicted as dogmatically orthodox or cautious at best, examining the content of the classroom reveals a much more nuanced consideration in the fields of optics, astronomy, cosmology, time keeping, and arithmetic. The evidence from Grassi's lectures and publications in the early seventeenth century demonstrate the extend to which Jesuits were able to participate fully in the developments in the history of science during the early modern period. This dissertation demonstrates that the Society of Jesus was extensively involved in the minutia of early modern debates about the certainty of mathematics, the distribution and substance of the cosmos, the nature of comets and other celestial pheomena, debates about the nature of light and sight, and many more contemporaneous issues of interest to the scientific community. Through a comparative textual analysis of Grassi’s lecture notes as well as his normative publications, this dissertation argues that Jesuit science and science education was neither isolationist nor backward. Rather early modern Jesuit mathematicians such as Grassi were able to not only engage at the highest level of debate with luminaries such as Galileo Galilei, and were also responsible for building concensus around challenging issues and topics.