Some materials have the property of rotating the oscillation direction of the electromagnetic field of linearly polarized light; this property is called optical activity. Molecules or crystals that are chiral are optically active, but the degree of optical activity depends on the particular material. Although color is an aesthetically pleasing optical effect and can also have many uses, there are other interesting optical properties of materials that do not necessarily involve color. The chapter discusses optical activity can be used to advantage in a liquid crystal display (LCD) device. In a field-effect LCD, each digit of the display device is seven pairs of electrode sandwiches. One important factor in this display involves plane polarized light. Outside light passing into a LCD device first passes through a polarizer. Birefringence in an anisotropic material arises because unpolarized incident light is split into polarized components because the speed of light is different in different directions.