Are humans the only dreamers on Earth? What goes on in the minds of animals when they sleep? When Animals Dream brings together behavioral and neuroscientific research on animal sleep with philosophical theories of dreaming. It shows that dreams provide an invaluable window into the cognitive and emotional lives of nonhuman animals, giving us access to a seemingly inaccessible realm of animal experience. David Pea-Guzmn uncovers evidence of animal dreaming throughout the scientific literature, suggesting that many animals run "reality simulations" while asleep, with a dream-ego moving through a dynamic and coherent dreamscape. He builds a convincing case for animals as conscious beings and examines the thorny scientific, philosophical, and ethical questions it raises. Once we accept that animals dream, we incur a host of moral obligations and have no choice but to rethink our views about who animals are and the interior lives they lead. A mesmerizing journey into the otherworldly domain of nonhuman consciousness, When Animals Dream carries profound implications for contemporary debates about animal cognition, animal ethics, and animal rights, challenging us to regard animals as beings who matter, and for whom things matter.