Light is mystical. Yet, its behaviour is so fascinating. It is difficult to comprehend light to a single entity. In this unit, we learn it in two different scientific aspects called ray optics and wave optics. Ray optics deals with light that is represented as a ray travelling in straight lines. The geometrical constructs get the permanence to understand the various characteristics of light. In wave optics, we study about the phenomenon associated with the propagation of light as a wave. First, let us learn the ray optics followed by the wave optics.