Characterized as a book on "planetology," this volume is based on a research study by Stephen Dole done for the RAND corporation and is an admirably thorough analysis — and a technical one — of all the physically significant environmental characteristics necessary to sustain life as we know it on planete other than earth. Thus, statistics tell us that there must be some 600 million habitable planets in our galaxy, of which some 50 are habitable ones within 100 light years, and that Alpha Centauri, the star system nearest us, has one chance in 9.3 in having a habitable planet available. An attempt has been made to broaden the appeal of the study, but it remains essentially valuable for the science-oriented person with a strong interest in the theoretic possibilities of humanoid extraterrestrial life. A specialized book in astronomy.