Quantum mechanics is one of the most successful theories in the history of science. After more than a century of scrutiny, no physical phenomenon has been found to be in violation of its predictions. In optics, we can carry out experiments where light consists of a single “photon” and even manipulate the interaction of a single “photon” with a single atom. The objectives of this book are two-fold. On one hand, the foundation of quantum mechanics and the laws of quantum theory are discussed. On the other hand, novel applications of these ideas to modern and evolving fields of quantum communication and quantum computing are presented, with as little mathematics as possible. The target audience for this text is clearly undergraduate students in physics. But anyone curious about contemporary subjects in quantum physics (cryptography, teleportation, computing) will profit from reading this book.