This chapter is a general introduction to the properties and applications of gallium nitride (GaN) and related materials. In the first part, after an historical background on the relevant milestones of nitrides research, the most important structural and electrical properties of the materials will be described. A special emphasis will be given to InGaN quantum wells and AlGaN/GaN heterostructures, which are important systems for light‐emitting diodes (LEDs), laser diodes (LDs), and high electron mobility transistors (HEMTs). In the second part, the main applications of nitride materials for both optoelectronic devices and power‐ and high‐frequency electronics will be described, mentioning the most critical issues of GaN‐based technologies, which will then be illustrated in detail in the rest of the book.