Black holes are believed to lie at the heart of some of the most luminous objects in the universe, including quasars and the enigmatic gamma-ray bursts. I will describe what a black hole-- the most extreme prediction of Einstein's theory of gravity-- really is. I will talk about how it might be possible to get energy out of a black hole-- but only if it is spinning. In addition, I will discuss how a black hole can shine more brilliantly than an entire galaxy.