The Hall effect is observed when a magnetic field is applied to a metal through which a current flows: The current carriers are deflected in the field, giving rise to a transverse electric field. In a ferromagnetic metal the embedded magnetic moments produce an anomalous Hall effect. Because it depends on both electronic and magnetic properties of the metal, the anomalous Hall effect has become a useful experimental tool for solid-state physicists. In our laboratory in Jülich, for example, we have used the effect to study extremely thin magnetic layers and to observe the propagation of conduction electrons in a metal.