This book describes a wide variety of speculations by many authors about the consequences for humanity of coming into contact with extraterrestrial intelligence. The assumptions underlying those speculations are examined, and some conclusions are drawn. The book emphasizes the consequences of contact rather than the search, and takes account of popular views. As necessary background, the book also includes brief summaries of the history of thinking about extraterrestrial intelligence, searches for life and for signals, contrasting paradigms of how contact might take place, and the paradox that those paradigms allegedly create.