Optical materials are used in the construction of devices that guide light in some way. Optical materials can also be used to attenuate, or decrease the intensity of light. Optical materials are used to transmit light, not only visible, but also light in the infrared and ultraviolet ranges. Historically, glass was the first optical material used in the fabrication of imaging systems, such as telescopes and microscopes. Most glass used in optical applications is based on silica with other materials mixed in to control various optical properties. The chapter introduces different classes of materials used in the fabrication of optical devices and instruments. Optical components are fabricated by grinding and polishing these optical materials. Optical polymers are transparent plastics, which can be used for lenses, optical storage media, such as compact discs, and for lightguides, metallized reflectors, optical fibres, and couplers. The chapter presents the types of lenses used in building optic and optical fibre devices and instruments.