The Franciscan and Dominican orders, originating in the thirteenth century, developed novel ways of understanding the natural world. Through an examination of the role of animals in their preaching, this thesis highlights one channel through which such views passed to the medieval laity. The friars presented their audiences with many examples from the “book of creation”—signs in the natural world that God left for mankind. In thirteenth-century sermons, mendicant preachers emphasized the instructive power of such signs by declaring that animals were exemplars of correct behavior towards both God and mankind, useful analogies for understanding orthodox doctrine, and agents that punished sinners. This new image of animals as a fundamentally “good” extension of God’s “book of creation” was ultimately an extremely significant persuasive tool that the friars turned to in their attempts to save the souls of medieval Europeans, even in the face of clear resistance.