In this book we have paid greater attention to explaining the essence of the absorption and scattering of x-rays in materials and drawing the laws, placing emphasis on the interaction between x-rays and materials.And great care has been taken that these should contribute to the solution of the basic theoretical development and practical problems in this field. We think scientific and theoretical contents dealt with in this book will contribute to the study of physical processes arising in the research on the absorption and scattering of x-rays in a material.Since the absorption and scattering of an x-ray in a material are phenomena which occur together in the relation of accompaniment, they can never be studied separately.