 The challenge of uniting quantum theory and general relativity in a successful theory of quantum gravity has arguably been the greatest challenge facing theoretical physics for the past eighty years. One avenue that has seemed particularly promising is the attempt to apply quantum theory to black holes. This is in part because, as purely gravitational entities, black holes present an apparently simple but physically important case for the study of the quantization of gravity. Further, because the gravitational force grows without bound as one nears a standard black-hole singularity, one would expect quantum gravitational effects (which should come into play at extremely high energies) to manifest themselves in the interior of black holes. 