Popular science writer Philip Ball explores a range of sciences to map our answers to a huge, philosophically rich question: How do we even begin to think about minds that are not human? Sciences from zoology to astrobiology, computer science to neuroscience, are seeking to understand minds in their own distinct disciplinary realms. Taking a uniquely broad view of minds and where to find them—including in plants, aliens, and God—Philip Ball pulls the pieces together to explore what sorts of minds we might expect to find in the universe. In so doing, he offers for the first time a unified way of thinking about what minds are and what they can do, by locating them in what he calls the “space of possible minds.” By identifying and mapping out properties of mind without prioritizing the human, Ball sheds new light on a host of fascinating questions: What moral rights should we afford animals, and can we understand their thoughts? Should we worry that AI is going to take over society? If there are intelligent aliens out there, how could we communicate with them? Should we? Understanding the space of possible minds also reveals ways of making advances in understanding some of the most challenging questions in contemporary science: What is thought? What is consciousness? And what (if anything) is free will? Informed by conversations with leading researchers, Ball’s brilliant survey of current views about the nature and existence of minds is more mind-expanding than we could imagine. In this fascinating panorama of other minds, we come to better know our own.