  Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are
starting to provide interesting or even unique new insights in observational
cosmology. GRBs represent a new way of identifying a population of star-forming
galaxies at cosmological redshifts. GRB hosts are broadly similar to the normal
field galaxy populations at comparable redshifts and magnitudes, and indicate
at most a mild luminosity evolution out to z ~ 1.5 - 2. GRB optical afterglows
seen in absorption provide a powerful new probe of the ISM in dense, central
regions of their host galaxies, complementary to the traditional studies using
QSO absorbers. Some GRB hosts are heavily obscured, and provide a new way to
select a population of cosmological sub-mm sources, and a novel constraint on
the total obscured fraction of star formation over the history of the universe.
Finally, detection of GRB afterglows at z > 6 may provide a unique way to probe
the primordial star formation, massive IMF, early IGM, and chemical enrichment
at the end of the cosmic reionization era.
