This appendix explains quantum effects: uncertainty, entanglement, and superposition; and explains how these effects form the basis of quantum sensing, computing and communication. This appendix summarizes the history and debates of wave mechanics, which was developed at the start of the Twentieth Century. Examples are given of macro-level quantum effects that the reader can observe in an attempt to start building an intuitive sense of quantum effects. These macro-level quantum phenomena are the dual-slit experiment, black-body radiation, and the characteristics of polarized light. Much attention is given to the characteristics of light, both because light provides examples of quantum effects but also because photonic emitters and sensors play a key role in quantum sensing, computing, and communication.