Professor Bondi discusses some of the myths that have grown up around various scientific theories and ideas, particularly special relativity and Mach's principle. His critical - and often light-hearted - approach to what are usually regarded as complicated ideas leaves the reader with the feeling that perhaps much of his subject is common sense after all. Professor Bondi's aim is to provoke thought, rather than to provide all the answers. He first discusses the limits of theory-making, the significance of depth and universality and the devising of effective tests for scientific theories. The relation of Einstein's theory to classical Newtonian mechanics is then considered, the author showing that relativity can be regarded simple as an extension of Newton's ideas on dynamics to the whole of physics. After deriving the equations of special relativity by the so-called k-calculus, he disposes rapidly of the 'clock paradox' and moves on to discuss general relativity, the significance of the result of Newman and Penrose concerning gravitational waves, the sources of gravitation and inertia, Mach's principles and the Hoyle-Narlikar relativity theory.