Reflection and transmission occur when electromagnetic waves incident on an interface between two different media. At the interface, a part of the incident wave reflects back and the other part penetrates into the other medium. Many applications in communication systems such as transmission of electromagnetic energy through waveguides, reflection of radio waves from the ionosphere, directing the electromagnetic energy by reflector antennas, and transmission through optical fiber cables are based on the reflection and transmission of electromagnetic plane waves. This chapter deals with reflection and transmission of electromagnetic waves for different polarizations of the incident wave. The negative refraction phenomenon is also discussed in this chapter. The topics of the chapter are supported by numerous illustrative examples and figures in addition to solved problems and homework problems at the end of the chapter.