Since ancient times people have been fascinated by the idea of extraterrestrial life; today we are searching systematically for it. Paul Davies's striking book examines the assumptions that go into this search and draws out the startling implications for science, religion and our world view should we discover that we are not alone. Evidence of the existence of extraterrestrial life would confront us with many fundamental questions. Has life spread out from a single source or arisen in several places independently? Is it a 'miracle', an improbable accident or an inevitable result of the laws of biology and physics? Is there a purpose, a general trend from simple to complex, from microbes to mind, built into the scheme of things? And what would the existence of conscious and intelligent aliens tell us about ourselves and our place in the universe? For generations, such issues have been classified under theology or science fiction; Paul Davies demonstrates how they are now being illuminated by scientific reasoning and hard-headed research.