Gaia will provide by the end of this decade astrometry and
photometry for a billion stars in the Milky Way down to V~20,
and radial velocities for 150 million stars down to V<17,
leaving a glaring hole in an otherwise unbiased catalog of the
stellar populations of the Galaxy. BigBOSS is the only
project/instrument capable of filling in the Gaia gap, providing radial
velocities and chemistry for tens of millions of faint Milky Way stars.
Those stars have the key to characterize the potential well of the dark
halo of the Milky Way, understand the formation, accretion history,
and early evolution of the Galaxy, and finding the oldest stars
with the most primitive compositions. I will summarize results
from SDSS and other ongoing surveys, describe the latest results
from BOSS on halo stars, and glance at what BigBOSS could do for
the Galaxy.