  We study the properties of very faint, sub-L* Lyman break galaxies at z~2-5 -
thus far a largely neglected but numerically and energetically very important
population. We find that the LBG luminosity function undergoes
luminosity-dependent evolution: the number of luminous galaxies remains
constant while the number of faint ones grows with time. The total UV
luminosity density increases with cosmic time from at least z~5 until reaching
a peak or a plateau around z~2 - behaviour that is governed by the sub-L*
galaxies in the LF's "faint tail". Using broadband SED fitting we find a
nearly-linear relationship between SFR and galaxy stellar mass at z~2. A
typical L* LBG at z~2 shows a stellar mass of ~10^10M_sun, remarkably similar
to the bimodality mass at low redshift. This similarity suggests that the
mechanisms responsible for the galaxy bimodality at low-z may have also been at
play at z~2.
