"Extraterrestrials may not have invaded the Earth physically but for centuries they have done so mentally. In many a guise they have appeared not only in works of fiction but also in serious astronomical, philosophical and theological debate. It is impossible to open Michael Crowe's handsome and fastidiously prepared anthology of primary sources without being drawn into endlessly fascinating disputes concerning the possibility and character of extraterrestrial life. Savoring the many twists and turns in controversies that have extended far beyond the confines of popular astronomy, Professor Crowe has provided students and experts alike with a generous and indispensable resource. It is difficult to resist his invitation to investigate for ourselves the innumerable, and often surprising, ways in which the idea of intelligent life on other worlds has shaped and been shaped by perennial Earthly concerns." --John Hedley Brooke, Andreas Idreos Professor Emeritus of Science and Religion, University of Oxford.