Bionics is defined here as the science of machines and systems that work in the manner of living things. The field is new and even the experts engaged in it have not described its boundaries to their own satisfaction. This probably accounts for the fact that this book as well as Marteka's Bionics (1965, p. 328, J-120) have the aspect of piecemeal, state of the art reports. Mr. Halacy makes many references to symposiums, speakers and includes long quotations. In one way, this increases the value of his book. On the other hand, it makes for heavier going than Marteka, who wrote on this subject with what seems a more realistic concept of attention spans at this age level. Mr. Halacy also over-argues the point that mankind has been slow witted in failing to appreciate the invented accomplishments arrived at through the study of nature. In view of the 20th century's technical competence, this repeated charge becomes not only monotonous but a distortion. Both the books report many fascinating projects in progress. Halacy lists more, while Marteka reports fewer in greater detail.