  The galaxy population hosting long-duration GRBs provides a means to
constrain the progenitor and an opportunity to use these violent explosions to
characterize the nature of the high-redshift universe. Studies of GRB host
galaxies in emission reveal a population of star-forming galaxies with great
diversity, spanning a wide range of masses, metallicities, and redshifts.
However, as a population GRB hosts are significantly less massive and poorer in
metals than the hosts of other core-collapse transients, suggesting that GRB
production is only efficient at metallicities significantly below Solar. GRBs
may also prefer compact galaxies, and dense and/or central regions of galaxies,
more than other types of core-collapse explosion. Meanwhile, studies of hosts
in absorption against the luminous GRB optical afterglow provide a unique means
of unveiling properties of the ISM in even the faintest and most distant
galaxies; these observations are helping to constrain the chemical evolution of
galaxies and the properties of interstellar dust out to very high redshifts.
New ground- and space-based instrumentation, and the accumulation of larger and
more carefully-selected samples, are continually enhancing our view of the GRB
host population.
