This book gives a comprehensive account of modern x-ray science based on the use of synchrotron radiation and x-ray-free electron lasers (XFELs), presented against the historical background of the puzzling nature of light, and culminating in quantum electrodynamics (QED) and quantum optics. It covers the physical foundations of the creation, properties, and detection of x-rays, uniquely emphasizing how the classical wave theory emerges from the photon concept of QED in lowest order. It then presents the formulation of the interactions of x-rays with atomic matter from both semi-empirical...