Reflection high-energy electron diffraction is one of the most powerful tools used in surface structural analysis to monitor epitaxial growth. This book serves as an introduction to RHEED for beginners and details experimental and theoretical treatments for experts. First, the principles of electron diffraction are explained, with many examples of RHEED patterns described for beginners. The second part contains in-depth descriptions of RHEED theory. Finally, applications of RHEED are explained with many examples.