  In this lecture I give an introduction to the rotational energy extraction of
black holes by the electromagnetic Blandford-Znajek process and the generation
of relativistic jets. After some basic material on the electrodynamics of black
hole magnetospheres, we derive the most important results of Blandford and
Znajek by making use of Kerr-Schild coordinates, which are regular on the
horizon. In a final part we briefly describe results of recent numerical
simulations of accretion flows on rotating black holes, the resulting
large-scale outflows, and the formation of collimated relativistic jets with
high Lorentz factors.
