At least from a microscopic (quantum mechanical) standpoint the description of time-dependent physical phenomena in the realm of magnetic nanostructures is still in its infancy, is mostly terra incognita, in particular when physical properties have to be described that occur only on a pico-or femtosecond scale. However, since quite a few of these properties, such as currentinduced switching (nano-to picosecond regime) or pump-probe experiments, e.g., in connection with time-resolved Kerr measurements (pico-to femtosecond scale), might change completely the direction of research in the field of magnetic nanostructured matter, an attempt is made here (a) to extend the Kubo formulation to the regime of femtosecond magneto-optics and (b) to introduce the time-dependent Dirac equation in the presence of an external electro-magnetic field in order to describe time-dependent "spin-polarized" phenomena such as spin currents and spin torques.