This appendix situates quantum technologies as a product of the merger of quantum mechanics, the theory of the very small; and information theory, the theory of how information is communicated and quantified. These intersections of these fields create quantum information science (QIS), provide a basis for understanding quantum sensing, computing, and communication. This appendix explains quantum scale and starts an exploration as to why effects at the quantum scale are so radically different from humans' day-to-day experience.