Periodic nanostructures in photonics facilitate a far-reaching control of light propagation and light–matter interaction. This article reviews the current status of this subject, including both recent progress and well-established results. The primary focus is on the basic physical principles and potential applications associated with the existence of Bragg scattering, photonic band structures, and engineered effective-medium properties in periodic dielectric and metallo-dielectric systems. In addition, we discuss advantages and limitations of various theoretical and numerical approaches as well as of those fabrication techniques that have specifically been developed for this field.