The histories of nonhuman animals and how they shaped human history are pressing and important issues that lie at the forefront of historical scholarship today. The project addresses these questions by bringing animals and their diseases from the margins to the center of medical historical enquiry, and analyzing the traces that they left on the medical historical record. Spanning Western Europe and North America, it goes beyond the existing study of animals as experimental material or transmitters of diseases to humans, to explore formerly unrecognized roles that animals performed at the intersections between human medicine, veterinary medicine, and the life sciences. These included: spontaneous (rather than laboratory-created) analogues of human diseases, tools for thinking comparatively about medical and biological problems, shapers and products of disease environments, disease victims, forgers of research networks, and carriers of personal and professional ambitions. Analysis of these animal roles not only advances understandings of animals within medicine, but also opens up new perspectives on what constituted medicine in particular times and places.