The introduction provides an overview of current theoretical concepts in animal and environmental studies for examining historical equine-human relations and previews the book chapters. The author argues that the embodied experiences of historical horses created real-world entanglements with the political and social structures that aimed to define or control them. This animal imprint, made visible in governance structures, was one way that animals participated in early modern social relations and imperial ecologies, and also gave rise to numerous possibilities for feral or counter-intentional responses within an expanding early modern empire.