Recent studies of the volume-averaged history of stellar birth
are pointing to an era of intense star formation at z
1-1.5.
The optical datasets imply that a fraction close to 65% of the present-day
stars was produced at z >1, and only 25% at z >2. About
half of the stars observed today would be more than 9 Gyr old, and only 10%
would be younger than 5 Gyr.
(6)
There is no ``single epoch of galaxy formation'': rather, it appears that
galaxy formation is a gradual process.
Numerous uncertainties remain, however, particularly the role played
by dust in obscuring star-forming objects.
Our first glimpse of the history of galaxies
to z ~ 4 leads to the exciting question of what happened before.
Substantial sources of ultraviolet photons must
have been present at z 
5 to keep the universe ionized,
perhaps low-luminosity quasars
[23]
or a first generation of stars in
dark matter halos with virial temperature Tvir ~
104-105 K
[42],
[22]. Early star
formation provides a possible explanation for the widespread existence of heavy
elements in the Ly
forest
[9],
while reionization by QSOs may
produce a detectable signal in the radio extragalactic background at meter
wavelengths
[36].
A detailed exploration of such territories must
await projected facilities like the Next Generation Space Telescope
and the Square Kilometer Radio Telescope.
Support for this work was provided by NASA through ATP grant NAG5-4236.