Abstract In a short passage in Generation of Animals iii 11, 761b16-24, Aristotle appears to argue for the existence of life on the moon, or what commentators call ‘fire animals’. Just what this passage is supposed to mean is far from clear. This paper provides the background for Aristotle’s notion of fire animals in his predecessors, including Plato and the Presocratics, and then traces the theme into late antiquity. The paper also integrates the topic of fire animals into Aristotle’s natural philosophy. Finally, the paper demonstrates that Aristotle’s remarks on fire animals provide a unique window into his natural philosophy, particularly his cosmology.