Are comets, meteorites, and dust the stuff of life on Earth? Did life appear just once in 5 billion years? Or did it follow some principle of evolution and appear at several distinct periods, raising the possibility that life can exist elsewhere in the universe? Emmanuel Davoust, an internationally known specialist on galaxies, explores these provocative questions as well as such major themes and topics of debate as prebiotic chemistry and paleovisits, in this lucid investigation of the continuing search for extraterrestrial life. The search for life in the universe begins at the "water hole," a frequency band that radio astronomers have been exploring for more than two decades in the hope of detecting a signal of artificial origin amid the natural noise of our galaxy. The number of possible targets is huge, and so far we have hardly listened at all. Despite the silence, many search projects based on the hope of eventually detecting signals from other civilizations are underway. Davoust provides a rich yet succinct basis for understanding the stages of life in the cosmos - evolution from the Big Bang to the formation of elements and planets; organic molecules in interstellar space, meteorites, and comets; prebiotic chemistry in Saturn's largest satellite; possible primitive life in Mars' substratum; and the notion of evolved forms superior to ourselves. Above all, he points out, the search for life beyond Earth provides a valuable perspective, teaching us to look at our planet and at ourselves "through a stranger's eyes." Davoust also covers such intriguing terrain as the demography and sociology of extraterrestrials. He provides a nontechnical account of search strategies, listening projects, and the debates they engender - including the "Proxmire effect," Carl Sagan's petition, and Fred Hoyle's interstellar bacteria.