This section reviews the basic technological characteristics of laser and laser diode. The purpose here is to help understand the case analysis of Part II. Therefore, the technological details are limited to a minimum as much as possible. However, there will still be a good portion of technical explanation of laser diode in this chapter. Hence, you may wish to treat this chapter as a dictionary by skimming through this chapter and come back if you do not understand something technological while reading the case analysis. First, this chapter describes the characteristics of a laser and its basic principles and then outlines the technological features of a laser diode. It then provides an examination of the application and market of laser diodes.