How do signals such as electromagnetic fieldsField, musicMusic, or water disturbances propagate from one place to another? The answer is by waves and this makes wave motion an important area to understand in physics. All waves have certain characteristics in common. However, other characteristics can be very different from one type of wave to another. In this chapter we use light as an example of one type of wave. Its physical properties are significantly different from those of soundSound waves discussed in the following chapter. Some of the themes of the chapter are represented in Figs. 11.1, 11.2, 11.3, 11.4, 11.5 and 11.6. Figure 11.1 shows circular waves in a liquid. Figure 11.2 shows a set of mirrors. Figure 11.3 shows a child looking ather reflection in a mirror. Figure 11.4 shows dispersion and reflection of white light by a prism. Figure 11.5 shows an interference pattern of light going through a single slit. Figure 11.6 shows an interference pattern of light by a thin film of oil.