The Gaia Mission is making the most precise measurements ever made of
stars. These measurements have the promise to resolve physics issues
with the Solar System, stars, and the Milky Way, among others. One hope
is that the Mission's kinematic measurements might give us an image of
the dark matter in the Milky Way or produce results that identify the
detailed physical characteristics of the dark matter particle. I will
explain how the Mission works, and how it might deliver on these hopes. I
will also show evidence we have already found in the data for a
dark-matter substructure orbiting in the Milky Way halo.