Quantum mechanics is one of the pillars of contemporary physics; it is the mathematical language necessary to describe nature at the microscopic level. The founders realized that their formulation implies new properties of nature that are far from intuitive, for example a special class of correlations we call entanglement. When quantum mechanics was formulated in the 1920s, individual control of an atom or electron was not possible. Physicists devised imaginary “thought” experiments aimed at demonstrating the principles and predictions of quantum mechanics in the microscopic world. This changed with the development of traps for electrons, ions, and individual atoms in the 1970s and 1980s. In the 1990s, working with ions and individual atoms, it became clear that the entanglement of quantum mechanics could be used for information processing, motivating the development of quantum information, one of the largest areas of technological and scientific growth today.