This paper explores the genre of Ottoman plague treatises of the fifteenth and sixteenth centuries with a view to tracing the changes in the learned elite's medical knowledge concerning this disease. Clearly prompted by the increasing prominence of plague in Ottoman lands, these treatises tried systematically to present, analyze, and synthesize the available knowledge. So far largely discredited or ignored as a body of genre and indeed consisting almost entirely of unpublished manuscripts, Ottoman plague treatises constitute an immense body of literature and are an invaluable source for the student of the plague. Written by the leading Ottoman intellectuals-jurists, physicians, historians, and scholars-- these tracts were not simply copies of each other, but reflected dramatic changes in medical conceptual schemes, the implementation of new methods, and integration of new empirical observations into such schemes by means of such methods. Through an analysis of prominent examples of the genre, the paper will demonstrate that these treatises differed dramatically from the earlier works composed in the Islamic world during and immediately after the Black Death. Contrary to what is commonly held in the contemporary scholarship, these works reflect a clear recognition of notions of contagion. These ideas, which were circulating in the early modern Mediterranean world found their way to the Ottoman medical literature, around the same time as Renaissance scholars in Italian city-states developed similar perspectives. Furthermore, the paper will also show how these new notions of contagion gained prominence against other competing medical and non-medical explanations on the spread of this disease. Finally, it will stress the significance of the swift acceptance of these notions by the medical elite and how they were gradually harmonized and made compatible with the tenets of Islamic law, which, in respect of plague, became the basis for legal policies of the early modern Ottoman state in the late sixteenth century.