[In Extra-Terrestrial Civilizations] Asimov turns his talents for clear explanations of complex scientific subjects to the question of the existence of extraterrestrial life…. The chemical and physical bases for life are discussed in detail but never beyond the comprehension of high school students. If alien life exists, as Asimov believes it does, why have we not found any evidence of it? Asimov theorizes that cosmic distances between even the nearest stars, not to mention galaxies, are so great that visitations are highly unlikely…. This clearly written discussion of a topic of interest to many young people joins other good books on this subject such as Who Goes There? by Edward Edelson … and Ian Ridpath's Messages from the Stars….