In Lucretius' De rerum natura, animals are fundamentally like humans and deserve to be treated accordingly. Animals also have much to teach us, including about how to treat each other and, indeed, (other) animals. That is not merely poetic imagery, but also scientific argument. Lucretius' analysis of animal nature is thoroughly integrated with his broader philosophical arguments and integral to many. Animals likewise serve as moral exemplars in his didactic programme and even as symbols of it. Positing a continuum of life, rather than a hierarchy of being, Lucretius thus offers a thorough, systematic challenge to the anthropocentric worldview exemplified by Plato, Aristotle and the Stoics. His position on animal intelligence and its ethical implications is an original contribution to the Epicurean tradition and a landmark in the history of ideas. It prefigures modern debates on subjects ranging from cognition and bioethics to ecology.