Over the course of the twentieth century, the relationship between Americans and their domestic animals has changed dramatically. In the 1890s, pets were a luxury, horses were the primary mode of transport, and nearly half of all Americans lived or worked on farms. Today, the pet industry is a multibillion-dollar-a-year business, keeping horses has become an expensive hobby, and consumers buy milk and meat in pristine supermarkets. Veterinarians have been very much a part of these changes in human-animal relationships. Indeed, the development of their profession―from horse doctor to medical scientist―provides an important perspective on these significant transformations in America's social, cultural, and economic history.