In this highly original, novel and integrated approach to theoretical reasoning in physics, Malcolm Longair has produced a text that illuminates the subject from the perspective of real physics as practised by research scientiste. The approach concentrates upon the basic insights, attitudes and techniques that are the tools of the modern physicist, in a manner that conveys the intellectual excitement and beauty of the subject. The book is intended as an alternative approach to the way in which basic physics is normally presented. It is not a substitute for the standard approach to presenting physics but, rather, deepens understanding and appreciation of the essence of the subject. It is assumed that the reader has some grasp of university physics, and the book is best used as a supplement to the final years of an undergraduate course in physics. By means of a series of seven case studies, essentially the whole of an undergraduate physics course is reviewed from the point of view of how the concepts came about. This approach illuminates the intellectual struggles to attain understanding of some of the most difficult concepts in physics. The case studies include the origine of Newton'S law of gravitation, Maxwell's equations, mechanics and dynamics, linear and nonlinear, thermodynamics and statistical physics, theorigins of the concept of quanta, special relativity and general relativity, and Cosmology. The approach is the same as that in the highly acclaimed first edition, but the complete text has been revised and many newtopics introduced. The objectives are one to provide an integrated view of the whole subject and to illustrate by the use of historical case studies a number of important lessons: there is no single best way of solving a physics problem; individual thinking is essential to success; a central role is played by hard work, experience and above all imagination in the solution of frontier research problems; and creativity in the sciences is not so different from that in the arts.