This dissertation examines the surge in writing on preventative medicine in Europe in the later Middle Ages. It offers an analysis of the regimen sanitatis genre, which became almost synonymous with writing on preventative medicine in the Latin West from the thirteenth to the fifteenth centuries, and argues that regimina contributed to a reconceptualization of medicine as a textual practice; an interaction between body and text. The dissertation explores how this new type of textual medicine interacted with other literary genres and how it conceptualized and developed thinking about subjecthood, gender, society, and human relationships. Chapter 1 considers what it means to write a personalized text. It examines how medieval medical theory, which stated that every individual required tailor-made medical advice, was used by regimina written for one named individual subject. I argue that despite ostensibly claiming to tailor advice to an individual’s body, regimina were more interested in accounting for numerous physical contingencies and possible readers. In doing so, they taught their audience how to read and assess their own bodies as mediated by the regimen’s framework. Chapter 2 examines the little-known genre of preventative writing meant to ensure a healthy pregnancy. These pregnancy regimens had to grapple with prescribing rules for a body thought to be highly pathologized and fragile. In doing so they pushed the boundaries of traditional preventative writing and positioned themselves as alternatives to natural biological processes. I argue that authors of pregnancy regimina carved out a new role for textual medicine as providing an alternative to the works of Nature, and as competing with the whims of a subject dominated by unhealthy desires. The third and final chapter tracks medieval notions of collective social wellness as a consequence of the plague outbreaks of the fourteenth and fifteenth centuries. It argues that regimina written for plague prevention constructed a sense of social prophylaxis that was bound by a culture of reading. Plague regimina were interested in social taxonomies and the social makeup that allowed plague to run rampant in a society, and they advocated for the dissemination of preventative writing in an attempt to prevent the spread of plague through medical, theological, and psychological methods.