Many scholars investigating "animal studies" questions in the literature of the "long eighteenth century" misunderstand, misinterpret, malign, or simply ignore the religious contexts of that literature. For some, Christianity belongs in a category of outmoded historical discourses, an embarrassment of the past best scrubbed from our memory of serious thinkers like John Locke or René Descartes. For others, the Christian religion represents a kind of intellectual disease that has caused and facilitated the abuse and exploitation of animals for centuries. At best, Christianity is hardly mentioned in recent studies focused on eighteenth-century literature and animals despite the religion's driving force in the work of many, if not most, canonical authors in this period. In fact, beginning with the "animal soul" controversy in the seventeenth century, these writers always thought about animals and humanity's relationship with them in the context of religious beliefs, traditions, and communities.By attending to these discussions on their own terms, this dissertation reveals how Christian belief, tradition, and language were used to advance the cause of justice for animals in this period's texts and artworks. In contrast to scholars who characterize Christianity as the "most anthropocentric religion the world has ever seen," I argue that Christianity in this period taught moral humility, emphasized the potential for transformation, and worked to reform human communities to include animals in their vision of global flourishing. Christian writers like John Milton, William Cowper, and William Blake picked up on threads of English theology, particularly natural theology, to express kinship with animals. Others, like John Wesley, Alexander Pope, and Sarah Trimmer, drew on their Christian beliefs to argue on behalf of animal welfare. Preserved in Christian songs, poems, fables, allegories, and artworks resides the work of thinkers who employed biblical teaching and religious tradition to argue on behalf of animals, and their work must complicate the scholarly view of religious history and its relationship to the ecological crisis.