One of the most mysterious yet simple aspects of quantum mechanics (QM) is the behaviour of angular momentum, both of the familiar "orbital" variety and of the "intrinsic" variety called spin. The latter type has a copyright on the term "spin" in the language of Physics; even though in more colloquial usage "spin" is just another name for angular momentum, in Physics it has a special meaning. But before we can make that distinction, we must first remind ourselves of the definition and behaviour of angular momentum and see how it is tied to the magnetic moment of a charged particle.