This book was written about 20 years ago. Asimov's scientific rigour and marvelouly clear divulgative style guides uthe reader to what we know of the possible existence of extraterrestrial civilizations. Had he written this book today, he would have been less optimistic, perhaps, but most of his reasoning wouldn't have changed.

For once, a scientists explains the science related to a topic many ufologists love and hate. I believe it is a useful book, as it's a purely scientific approach that does not involve UFOs at all. I like the front cover design.