In the classification of materials the exact placement of optical materials is to some extent a matter of preference. The gallium arsenide light-emitting diodes are generally covered under semiconductors (see Chapter 10), but semiconducting gallium arsenide and other compound semiconductors have also been used for lasers. The optical properties of liquid crystals appear to fit better under polymers than with the optical materials. In the general broad field of optoelectronics, the optical and electronic properties of a given material often overlap. The optical properties of materials have become of more interest in recent years because of their application in the high-tech industries. The telecommunications industry is dependent on optical fibers. Lasers are used in many high-tech devices, and luminescence materials are widely used in many types of displays. In this chapter we will confine our presentation to refraction, reflection, absorption, luminescence, optical fibers, and lasers.