X-ray and electron diffraction methods are very useful for material researches. Various techniques have been developed for studying crystal structures, identifying and quantifying phases, determining crystal orientations and obtaining many other structural properties of materials. In this course, we will first introduce basic crystallography of materials and then discuss the fundamental concepts of diffraction, principle of diffraction, and the mathematical methods to solve the diffraction problems. Diffraction methods, practical considerations, and examples will be discussed in the lectures.