  As a byproduct of its search for the first star forming galaxies, NGST will
obtain high-quality spectra for thousands of galaxies in the redshift range z =
0 - 6 and beyond. Most of the galaxies will possess strong emission-line
spectra, and these spectra will provide a wealth of information on their star
formation rates, reddening, metal abundances, internal kinematics, and nuclear
activity. This will make it possible to construct a comprehensive picture of
the buildup of stars, metals, dust, and the nuclei of galaxies with
cosmological lookback time. This paper reviews what can be learned from the
spectra of distant emission-line galaxies. Simulations of NGST spectra are used
to explore the instrumental tradeoffss for these applications, and the
respective roles of NGST and groundbased surveys.
