  Deep, near-infrared imaging surveys have been motivated by the desire to
study the rest-frame optical properties and stellar content of galaxies at high
redshift. Here we briefly review their history, and illustrate one application,
using HST NICMOS imaging of the Hubble Deep Field North to examine the
rest-frame optical luminosities and colors of galaxies at 2 < z < 3, and to
constrain their stellar masses. The rest-frame B-band luminosity density at z =
2.5 is similar to that in the local universe, but the galaxies are evidently
less massive, with rapid star formation and low mass-to-light ratios. There are
few candidates for red, non-star-forming galaxies at these redshifts to the
HDF/NICMOS limits. We estimate a stellar mass density at 2 < z < 3 that is ~5%
of the present-day value, with an upper bound of <= 30%. Future headway will
come from wide-field ground-based surveys, multiplexing infrared spectrographs,
and new space-based facilities such as HST/WFC3 and SIRTF/IRAC.
