Abstract
The presence of supermassive black holes in galactic nuclei, both quiescent and active, is now well established. Advances in understanding the nature of the broad emission-line region make it possible to measure black hole masses in large numbers of active galactic nuclei (AGN). This in turn allows study of AGN properties as a function of black hole mass and Eddington ratio. Such studies should lead to a better understanding of the physics of AGN. The ability to measure black hole masses in QSOs also allows study of the relationship between black hole mass and host galaxy properties. Early results suggest that this relationship in QSOs at redshifts z ~ 2 was similar to that in nearby galaxies today.
