  Through a combination of deep wide-field imaging and multi-object
spectroscopy, the Next Generation Space Telescope will be able to chart with
unprecedented accuracy the evolution of cosmic structures after the `dark ages'
(z<5), when galaxies are thought to assemble and form the bulk of their stars.
In this talk I will discuss how NGST observations might determine the history
of the stellar birthrate in the universe and reveal the character of
cosmological ionizing sources at high redshifts.
