The sub-title is misleading since the existence of extra-terrestrial life is still only a statistical premise for most scientists. The one chapter (of 12) detailing the hot controversy about whether or not the Orgueil meteorite contains proof of organic matter from space does not include the latest discovery of the University of Chicago scientists who clearly determined that French plant life had been deliberately embedded in the meteoritic material they examined. Nevertheless, other chapters contain much interesting information about the extremes of life on earth, the hardiness of life, the nature of environments on the moon and Mars, the search for ""Optiman""--the kind of man-machine that must be part of the spacecraft system to make it operate efficiently over long periods of time. Often what is best appears in the notes to the chapters, and particularly in the appendices where there is a translation from the Russian of an intriguing analysis of what the mysterious 1908 ""meteor"" explosion over Siberia might really have been. Walter Sullivan's We Are Not Alone (McGraw-Hill-1964) is still the best survey of the subject.