With current interest in extraterrestrials at a peak, this book is a collection of original and reprinted articles advancing the latest scientific ideas as to the possible existence and nature of extraterrestrial intelligent life. Usually this subject is treated only in popular media, such as science fiction novels, movies, and television. Recently, however, scientists and researchers have begun to consider in earnest whether extraterrestrials really exist, whether they have evolved from simpler forms of life, whether they have evolved intelligence, and if so whether their modes of understanding the world are comparable to and congruent with our own. The contributors to this volume cover these topics, and also consider how we might communicate with aliens, and whether we would be able to understand the alien messages we might receive. Finally the authors, who include distinguished scientists, speculate whether the aliens might have a moral code, and what might be our moral obligations in the event any extraterrestrials were ever discovered.