  The physical properties of the faint blue galaxy population are reviewed in
the context of observational progress made via deep spectroscopic surveys and
Hubble Space Telescope imaging of field galaxies at various limits, and
theoretical models for the integrated star formation history of the Universe.
Notwithstanding uncertainties in the properties of the local population of
galaxies, convincing evidence has emerged from several independent studies for
a rapid decline in the volume-averaged star formation rate of field galaxies
since a redshift z~1. Together with the small angular sizes and modest mean
redshift of the faintest detectable sources, these results can be understood in
hierarchical models where the bulk of the star formation occurred at redshifts
between z~1-2. The physical processes responsible for the subsequent demise of
the faint blue galaxy population remains unclear. Considerable progress will be
possible when the evolutionary trends can be monitored in the context of
independent physical parameters such as the underlying galactic mass.

Astrophysics