  The concordance Cold Dark Matter model for the formation of structure in the
Universe, while remarkably successful at describing observations on large
scales, has a number of problems on galaxy scales. The Milky Way and its
satellite system provide a key laboratory for exploring dark matter (DM) in
this regime, but some of the most definitive tests of local DM await
microarcsecond astrometry, such as will be delivered by the Space
Interferometry Mission (SIM Planetquest). I discuss several tests of Galactic
DM enabled by future microarcsecond astrometry.
