  We discuss the synergy of Gaia and the Large Synoptic Survey Telescope (LSST)
in the context of Milky Way studies. LSST can be thought of as Gaia's deep
complement because the two surveys will deliver trigonometric parallax,
proper-motion, and photometric measurements with similar uncertainties at
Gaia's faint end at $r=20$, and LSST will extend these measurements to a limit
about five magnitudes fainter. We also point out that users of Gaia data will
have developed data analysis skills required to benefit from LSST data, and
provide detailed information about how international participants can join
LSST.
