The existence of intelligent extraterrestrial life has been a subject of debate since the dawn of recorded history. The Last Frontier, originally published in German in 1983 and now available in Helen Atkins's sensitive English translation, traces the development of the idea that Earth is not the only planet inhabited by intelligent beings, but that there might be a plurality or even an infinity of "worlds" with human or humanoid life. Focusing on the seventeenth to the twentieth century and taking into account theological, philosophical, scientific, popular, and literary writings from American, British, French, and German sources, Karl S. Guthke demonstrates the continuing importance of this question to the process of human self-definition.