Modern research has demonstrated that many stars are surrounded by planets—some of which might contain the right conditions to harbor life. This has only reinforced a question that has been tormenting scientists, philosophers and priests since Antiquity: Are there other inhabited worlds beyond our own? This book analyzes the many ways that humans have argued for and depicted extraterrestrial life over the centuries. The first known texts about the subject date from as early as the 6th century BC. Since that time, countless well-known historical characters like Lucretius, Aristotle, Thomas Aquinas, Cusanus, Bruno, Kepler, Descartes, and Huygens contributed to the debate; here, their lesser known opinions on the subject are studied in detail. It is often difficult for the modern mind to follow the thinking of our ancestors, which can only be understood when placed in the relevant context. The book thus extends its scope to the evolution of ideas about cosmology in general, as well as the culture in which these great thinkers wrote. The research is presented with the author's insights and humor, making this an easy and enjoyable read.