This book provides insight into the underlying basic theories and concepts in X-ray, light, and neutron scattering. The three scattering principles are systematically presented, together with a unified description based on elastic scattering of electromagnetic waves and the Schroedinger wave from matter. These explanations are presented with an introduction of their common Born approximation using a consistent set of symbols and terminology and with step-by-step derivations of equations. This book emphasizes the combined applications of these three scattering methods, wherever and whenever possible, as a very powerful methodology for characterization of internal structures of soft matters in the length scale ranging from subnanometers to a few 10 micron meters. These applications include explorations for evolution of hierarchically self-organized internal structures of a variety of soft matters, including cells, under diverse environmental conditions. This book will not only be an excellent resource for graduate students and academic researchers who analyze structures of soft matters and polymers, but it will also be useful for researchers in industries.