Interest in extrasolar worlds is not new. From the late 17th century until the end of the 19th, almost all educated people believed that the stars are suns surrounded by inhabited planets--a belief that was expressed not in science fiction, but in serious speculation, both scientific and religious, as well as in poetry. Only during the first half of the 20th century was it thought that life-bearing extrasolar planets are rare. This book, first published by Atheneum in 1974, tells the story of the rise, fall, and eventual renewal of widespread conviction that we are not alone in the universe. Its chapters dealing with modern views have been revised to reflect the progress science has made during the past 40 years, including the actual detection of planets orbiting other stars. In addition it contains a new Afterword, "Confronting the Universe in the Twenty-First Century," discussing the relevance of past upheavals in human thought to an understanding of the hiatus in space exploration that has followed the Apollo moon landings.