Jun Kawai studies X-ray physics and chemistry, since 1981, when he joined Prof. Gohshi's laboratory, the University of Tokyo, in order to study the chemical effects of X-ray emission spectra, then moved to Institute for Molecular Science for the theoretical studies of the solid state effects of X-ray spectra, then moved to the Institute of Industrial Science, the University of Tokyo, for the development of X-ray photoelectron diffraction, then moved to RIKEN (The Institute of Physical and Chemical Research) as postdoctoral fellow for studying the total reflection X-ray photoelectron spectroscopy (XPS) as well as particle-induced X-ray emission (PIXE), and then moved to Kyoto University, where he studies radiative Auger effect, X-ray fluorescence holography, blackbody radiation, pyroelectric X-ray generation, polarization of Compton scattering, and so on. He teaches "Quantum Spectrochemistry" in Kyoto University, and the present book is partly based on this lecture. He has beenan associate editor of a journal "X-Ray Spectrometry" from Wiley and was a member of the editorial advisory board of "Spectrochimica Acta Part B: Atomic Spectroscopy" from Elsevier for more than 20 years.