How does an electron flip a magnetic moment?

A magnetic moment is incapable of flipping a magnetic moment unless some damping mechanism is present. On the other hand a spin current can flip a moment, as we will demonstrate in this talk. A variety of quantum effects will be illustrated, using an easy-to-understand semiclassical treatment. Finally, resorting to strictly quantum mechanics, the time evolution of a spin current/magnetic moment system can be determined; the problem is similar to the standard 4th year textbook problem of a particle scattering off a square barrier/well. In this case the ``barrier/well'' responds, i.e. the moment `flips.' We outline how one can monitor the `flip' as a function of time.