This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores the diverse ways in which the language of purity figures in formations of equine breed as a component of human history under the conditions of modernity. It deals with horse breeds prior to the eighteenth- and nineteenth-century shifts in breeding practice that saw the development of the modern “purebred.” The book considers how eighteenth-century breeders negotiated systems of breeding knowledge in order to maintain genetic and aesthetic purity prior to modern understandings of how genes function. It provides considerations about questions of purity, inheritance, and the shift from landrace to pedigreed breeding, while tackling the interconnections between breed and regional and national identities. The book also considers the relationship between Welsh Cob breeding and Welsh human regional identity in which a celebration of impurity is understood as central to what is “Cob” and what is “Welsh.”