"..a clearly written textbook covering all the important aspects of the subject, emphasizing physical concepts and the richness of the field. I believe that it will become the standard reference text for students and anyone working in this area, so important in many parts of modern science, from the exploration of the atomic/molecular structure of matter with synchrotron radiation and free-electron lasers to that of the ultimate structure of elementary particles."Claudio Pellegrini, Professor Emeritus, UCLA