Of the three books dealing with UFO's (Incident at Exeter, Flying Saucers--Serious Business) to wing their way into the public eye this year, this is the most rational and logical. It is also not as easily read and unfortunately seems something of a rehash of Mr. Vallee's detailed observations in his earlier outstanding Anatomy of a Phenomenon (1965. p. 459). The authors intend this book to serve as ""a basis of reference and a general survey of the present state of the UFO problem and associated ideas."" It is technically oriented, once again analyzing reports and breaking them down scientifically. The first section gives an ""analysis of the patterns and general laws behind the observations by examining the spatial information and the topographic distribution of the sightings."" The second part deals with the variation of time in the frequency of the sightings and the third analyzes the reported objects according to type and offers a basis for further, comprehensive study. The book is a challenge to science: it will also challenge the layman who seeks to cope with its graphs, charts and technical terminology.