Light plays a central role in many applications of physics to real-world tasks. In particular, it is one of the chief tools for quantum metrology and quantum communication, and for reasons to be discussed in later chapters, it is a promising physical mechanism for implementing various quantum information processing tasks. So, this chapter gives an overview of classical optics, with particular emphasis to aspects of classical light which will have close analogs in quantum mechanics; since both quantum mechanics and optics are based on linear wave equations, there are many classical optical phenomena that can be used to simulate quantum-like behavior. Furthermore, polarization in a classical optical beam is mathematically identical to spin in a spin- \(1\over 2\) quantum system. So, both spin and polarization are two-state systems that can serve as physical implementations of quantum qubits. Similarly, the classical optical law of Malus can be viewed as the result of quantum state projections induced by measurements. For these and other reasons, it is profitable to treat quantum mechanics and optics in parallel.