The quasistellar object, the pulsar, the neutron star have all come onto the scene of physics within the space of a few years. Is the next entrant destined to be the black hole? If so, it is difficult to think of any development that could be of greater significance. A black hole, whether of “ordinary size” (approximately one solar mass,1 M⊙), or much larger (around106 M⊙to1010 M⊙,as proposed in the nuclei of some galaxies) provides our “laboratory model” for the gravitational collapse, predicted by Einstein's theory, of the universe itself.