This selection of essays covers a wide range of subjects connected with the physical sciences and their relation to human affairs. They are broadly conceived and directed to a generally interested audience rather than to specialists in particular areas. Some are written for the initiated, some are broad synopses of a branch of physics and are directed to the scientifically interested layman. Some deal with more philosophic questions such as Niels Bohr's ideas on complementarity, and others deal with the problems of science, ethics, and society. Hans Bethe writes as follows in the Foreword: "His summary articles on special topics are lucid and are 'popular scientific writing' at its best. The subject is made clear to physicists in other branches of physics and to the educated public by simplifying it, but without ever making a compromise with fundamental accuracy, as many popular writers on science do when they get enamored with their own imagery and forget the subject that they really want to explain. Viki's [Weisskopf's] main concern, as of most theoretical physicists, is the correct interpretation of the quantum theory.... This theme is already prominent in 1951 in his article 'Quantity and Quality in Quantum Physics.' Here he makes clear how a quantitative difference, such as the number of electrons of 6 in a carbon and 11 in a sodium atom, makes all the difference in the qualitative behavior of these two chemical elements. He also foresees, at this early time, some of the developments in biology related to DNA. "The summary article about electron theory (1949) is written essentially for physicists. He summarizes the great advances brought about by the renormalization theory which gives finite results for all observable quantities and is fundamental to modern field theory. His own field of nuclear physics is summarized in 'Problems of Nuclear Structure' (1961), in a simpler form in 'Nuclear Models' (1951). Weisskopf is always excited by important developments in physics even if he himself has not contributed. A major one of these [was described in] the 'Fall of Parity.' This article is a beautiful example of his ability to make things understandable without changing the essentials. In the 'Visual Appearance of Rapidly Moving Objects' he explains the discovery of Penrose that a rapidly moving object looks to us as it if had its natural shape and is not distorted by the Lorentz contraction as had previously been believed; in fact, without relativity theory it would look badly distorted. His 'How Light Interacts with Matter' is rich in new insights. "The theme is further developed in 'Physics in the Twentieth Century' and 'The Quantum Ladder.'... I don't know of any other place where the essential solidity of our world as governed by quantum theory is better explained, or the great richness of the phenomena caused by quantitative differences is shown with greater love." In addition to those mentioned above, the book includes a number of other essays. These concern physical theory (articles on the compound nucleus and on elementary particles), the human aspects of scientific research (articles on Niels Bohr and on Marie Curie), and biological theory (considerations of symmetry and function at the macromolecular level and of the quantum basis of organic reproduction). A final group of essays is concerned with such issues as the intrinsic value of science, the contributions of science to society, and scientific ethics. The latter is described by Bethe as "A most beautiful and concise statement of the scientist's creed."