This is the first book covering the theory, practicalities, and the extensive applications of neutron powder diffraction in materials science, physics, chemistry, mineralogy and engineering. Various highlight applications of neutron powder diffraction are outlined in the introduction, then the theory is developed and instrumentation described sufficient for a return to the applications. The book covers the use of neutron powder diffraction in the solution (hard) and refinement (more straightforward) of crystal and magnetic structures, applications of powder diffraction in quantitative phase analysis, extraction of microstructural information from powder diffraction patterns, and the applications of neutron diffraction in studies of elastic properties and for the measurement of residual stress. Additional theory to underpin these various applications is developed as required. Much of the material should be accessible to senior undergraduates in science and engineering, as well as to graduate students and more senior researchers with an interest in the technique.