  Recent data, e.g. from SDSS and 2dF, reveal a robust bi-modality in the
distribution of galaxy properties, with a characteristic transition scale at
stellar mass M_*~3x10^{10} Msun (near L_*), corresponding to virial velocity
V~100 km/s. Smaller galaxies tend to be blue disks of young populations. They
define a "fundamental line" of decreasing surface brightness, metallicity and
velocity with decreasing M_*, which extends to the smallest dwarf galaxies.
Galaxies above the critical scale are dominated by red spheroids of old
populations, with roughly constant high surface brightens and metallicity, and
they tend to host AGNs. A minimum in the virial M/L is obtained at the same
magic scale. This bi-modality can be the combined imprint of several different
physical processes. On smaller scales, disks are built by cold flows, and
supernova feedback is effective in regulating star formation. On larger scales,
the infalling gas is heated by a virial shock and star formation can be
suppressed by AGN feedback. Another feedback mechanism -- gas evaporation due
to photo-ionization -- may explain the existence of totally dark halos below
V~30 km/s. The standard cooling barriers are responsible for the loose upper
and lower bounds for galaxies: 10 < V < 300 km/s.
