There is little doubt that the last few years have been exciting times in
galaxy formation and evolution studies.
The remarkable progress in our understanding of faint
galaxy data made possible by the combination of HST deep imaging
[62]
and ground-based spectroscopy
[35],
[14],
[56] has
permitted to shed new light on the evolution of
the stellar birthrate in the
universe, to identify the epoch 1 
z
2 where most of
the optical extragalactic background light was produced, and to set important
contraints on galaxy evolution scenarios
[41],
[57],
[3],
[23]. The
explosion in the quantity of information available on the high-redshift
universe at optical wavelengths has been complemented by the detection of
the far-IR/sub-mm background by DIRBE and FIRAS
[28],
[16].
The IR data have revealed the optically ``hidden'' side of galaxy
formation, and shown that a significant fraction of the energy released
by stellar
nucleosynthesis is re-emitted as thermal radiation by dust. The underlying
goal of all these efforts is to understand the growth of cosmic structures
and the mechanisms that shaped the Hubble sequence, and ultimately to map
the transition from the cosmic ``dark age'' to a ionized
universe populated with luminous sources. While one of the important
questions recently emerged is the nature (starbursts or AGNs?) and redshift
distribution of the ultraluminous sub-mm sources discovered by SCUBA
[30],
[2],
[36],
of perhaps equal interest is the
possible existence of a large population of faint galaxies still undetected
at high-z, as the color-selected ground-based and Hubble Deep
Field
(HDF) samples include only the brightest and bluest star-forming objects.
In hierarchical clustering cosmogonies,
high-z dwarfs and/or mini-quasars (i.e. an early generation of
stars and accreting black holes in dark matter halos with circular velocities
vc ~
50 km s-1) may actually be one of the main source of UV photons and
heavy elements at early epochs
[44],
[25],
[26].
In this talk I will focus on some of the open issues and controversies
surrounding our present understanding of the history of the conversion of
cold gas into stars within galaxies, and of the evolution with cosmic time
of luminous sources in the universe. An Einstein-deSitter (EdS) universe
(
M = 1, 
= 0) with h =
H0 / 100 km s-1 Mpc-1 = 0.5 will be
adopted in the following.