This dissertation examines medieval fable collections from a critical animal studies perspective. Discussion is focused on relationships between humans and nonhuman animals, as portrayed in works written and circulated in Britain during the Middle Ages, particularly: Avianus's fables; the elegiac Romulus; Alexander Neckam's Novus Aesopus; Odo of Cheriton's Parabolae; the Fables ascribed to "Marie de France"; the Morall Fabillis of Robert Henryson; and William Caxton's Aesop. The dissertation offers close textual analyses of selected fables from these collections, some of which do not otherwise exist in modern English translation. Chapters are organized according to several themes: cohabitation between wild animals and humans; human domination of "working animals" such as dogs and donkeys; and the exploitation of domesticated animals such as sheep and birds for food and other resources. The concluding chapter analyzes two fables in which the species of characters changes drastically across versions, illustrating that animal characters' affordances shape the stories in which they appear, and that animal voices, in the counterfactual context of fable, may be invoked easily but heeded with difficulty. This dissertation argues that fables are highly heterogeneous and not reduceable to one message. Nevertheless, fables, in portraying nonhuman perspectives and voices, offer an alternative and sometimes oppositional discourse, imperfectly recuperated into dominant discourses about nonhuman animals in the Middle Ages.