  In recent years deep X-ray and infrared surveys have provided an efficient
way to find accreting supermassive black holes, otherwise known as active
galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical
surveys, find AGN obscured by high column densities of gas and dust. In those
cases, deep optical data show only the host galaxy, which can then be studied
in greater detail than in unobscured AGN. Some years ago the hard spectrum of
the X-ray "background" suggested that most AGN were obscured. Now GOODS, MUSYC,
COSMOS and other surveys have confirmed this picture and given important
quantitative constraints on AGN demographics. Specifically, we show that most
AGN are obscured at all redshifts and the amount of obscuration depends on both
luminosity and redshift, at least out to redshift z~2, the epoch of substantial
black holes and galaxy growth. Larger-area deep infrared and hard X-ray surveys
will be needed to reach higher redshifts and to probe fully the co-evolution of
galaxies and black holes.
