Understanding the Galaxy
  A general overview of the understanding of our Galaxy is presented following
the lines of its main structures: halo, disc, bulge/bar. This review is
emphasising some "Time Domain Astronomy" contributions. On the one hand the
distance and tangential motion of the stars are essential to this understanding
and are obtained through multi-epoch surveys, on the other hand the chemistry
of the stars, and their radial velocity are also key elements to map Galactic
(sub-)structures and unravel their history and evolution. Contemporary surveys
are revolutionising our view of the Milky Way and galaxies in general. Among
these, the Gaia mission excels by its precision astrometry of 1.3 billion stars
stretching through the Milky Way and beyond, providing the first 3D view of a
major part of the Milky Way.
