Einstein introduced quantum entanglement in 1935 and referred to it as “spooky actions at a distance” because it seemed to conflict with his theory of special relativity. Today, some refer to it as "the greatest mystery in physics" and the 2022 Nobel Prize in Physics was even awarded for experimental confirmation of the "spookiness." While the mystery is experimentally well-established, its solution remains elusive because it is commonly believed that quantum entanglement entails that quantum mechanics is incomplete, that the world works according to "spooky actions at a distance," that causes from the future create effects in the present, that there is "superdeterministic" causal control of experimental procedures, that people can correctly disagree on the outcome of one and the same experiment, and that a single experimental measurement can produce all possible outcomes. In this book, a rigorous solution to the mystery of quantum entanglement is provided that entails none of those things. The key to this seemingly impossible feat is - to use Einstein''s own language - a "principle" explanation that foregoes the need for any "constructive" explanation of quantum entanglement, such as those listed above. Ironically, the proposed principle explanation is Einstein''s own relativity principle as grounded in quantum information theory. So contrary to popular belief, quantum mechanics and special relativity are far from inconsistent, as both are a consequence of the exact same relativity principle.