X-ray and electron diffraction techniques are very useful tools for materials researchers. Various techniques have been developed for determining crystal structures, identifying the phases, quantifying the grain orientation and stress distribution in mechanically deformed materials, and evaluating the quality of thin films. In order to perform diffraction analysis and interpret the data, understanding the fundamental concepts of diffraction is essential. In this course, we will discuss the structure of matters, diffraction phenomena, diffraction methods, and the applications.