As argued many years ago by Hawking, black holes appear to violate quantum mechanics by destroying the reversibility of physical processes. Recent results in string theory however suggest a radically different picture of the black hole interior; instead of being just `empty space with a central singularity', it is now filled with a tangle of stringy matter. This picture would resolve the `information paradox' raised by Hawking, and show that quantum gravity effects are not confined to the planck length but instead stretch over distances that increase with the mass of the object being studied.