The most massive black-holes known reside in the centers of massive galaxies, and weigh as much as 1-10 billion solar masses. Accretion onto these super-massive black-holes is thought to power quasars, which are seen throughout most of the history of the universe. The most distant quasars known imply that some super-massive black-holes had already formed within the first billion years after the big-bang. A picture is now emerging where super-massive black-hole growth at these early epochs proceeds via accretion and coalescence within the context of a standard hierarchically merging cold dark matter universe. This picture naturally explains the observed abundance and luminosity distribution of high redshift quasars, as well as the properties of their spatial clustering. Of particular interest is the result that clustering statistics suggest that super-massive black-hole mass depend on the depth of the potential well in which it formed.