The health of horses, mules, and donkeys meant the difference between prosperity and penury, even life and death, for those who depended on them for agriculture, communication, travel, war, and spectacle in sixteenth-century Castile. Despite the social and symbolic significance of equids and the dependence of Castile and so many other human societies on their health, historians have attended far less to veterinary compared to human medicine. In this study, I examine sixteenth-century equine medicine (albeitería) through the figure of the equine doctor (albéitar herrador). I investigate what made these practitioners distinctive: their licensing and social organization, growing canon of texts and assertion of status, roles in legal medicine, and surgical skills. By relying on hippiatric treatises and lawsuit records, I am able to investigate their activities and knowledge in theory and practice. After an introduction, I examine their occupational hierarchy in Chapter Two. Though histories of albeitería emphasize the crown's licensing tribunal, I also attend to their communal institutions and informal cooperation. In Chapter Three, I survey the Castilian hippiatric treatises published in the sixteenth and seventeenth centuries to show how their authors developed a canon of texts, and by extension asserted the dignity and nobility of their art. I examine these works as trade manuals, destined for an equine doctor audience, and as medical literature, sharing theory and authorities with its human counterpart. In Chapter Four I explore the role of equine doctors and medical arguments in legal disputes. These suits suggest that the medical concepts most relevant in a forensic setting differ from the presentation of medicine in treatises. Finally, I argue in Chapter Five that surgical skills set equine doctors apart from other practitioners, and examine two such procedures as case studies: a specialized bleeding technique and cauterization. Whereas the first half of this study highlights connections between the occupational structure and intellectual tradition of human and equine medicine, the second suggests differences between the two in practice thanks to the nature of their patients and the ways people used equids.