 Quantum state superpositions and entanglement are two of the most fundamental concepts in quantum mechanics, and also two of its most misunderstood. And they are turning out to be the key to the next generation of quantum computing. In our first chapter, the microscopic, we covered the double-slit experiment that showed how photons and electrons display both wave and particle properties. It's called wave particle duality or complementarity. The key to the experiment was to observe what happens when we detect which of the slits a particle went through. For photons, we never explained how we could detect a photon without disturbing its path. So this final chapter brings us full circle, where we will cover in detail how this was done. In our second chapter on the atom, we covered Schrodinger's equation with its probability wave, Eisenberg's uncertainty principle, and Pauli's exclusion principle with electron spin. These constitute the base physics for understanding superpositions and entanglement. We'll cover exactly what quantum superposition and entanglement are. We'll cover Einstein's problem with quantum mechanics and its prediction that we will someday find hidden variables to explain entanglement. We'll cover a thought experiment designed to show that hidden variables cannot exist. It's called Bell's Theorem or Bell's Inequality. We'll cover a real experiment that uses entangled photons to create ghost images that produce a bell inequality. Along the way, we'll clear up a few misconceptions about Schrodinger's cat and the quantum eraser. We'll end with a look at quantum computing and how it directly manifests and leverages these quantum properties. Our first encounter with quantum superpositions will be the double slit experiment, so in preparation we'll cover some key characteristics of light polarization.