The neutron beam has been applied extensively in scientific studies and in industrial fields. Studies on neutron diffraction have been promoted for many materials, especially composite materials and light-element materials. In this book, the authors present topical research in the study of the principles, instrumentation and application of neutron diffraction. Topics discussed include neutron diffraction measurements for materials science; neutron diffraction studies of the isotopic effect in arrangement of hydrogen atoms in solid solutions of Ti-N-H, Ti-N-D and Ti-N-H-D systems; a study on the residual strain induced by thermal hysteresis in a composite material; and neutron diffractometers for fatigue study of engineering metals.