  We live in an age where an enormous amount of astrometric, photometric,
asteroseismic, and spectroscopic data of Milky Way stars are being acquired,
many orders of magnitude larger than about a decade ago. Thanks to the Gaia
astrometric mission and followup ground-based spectroscopic surveys in the next
5-10 years about 10-20 Million stars will have accurate 6D kinematics and
chemical composition measurements. KEPLER-2, PLATO, and TESS will provide
asteroseismic ages for a good fraction of those. In this article we outline
some outstanding problems concerning the formation and evolution of the Milky
Way and argue that, due to the complexity of physical processes involved in the
formation of disk galaxies, numerical simulations in the cosmological context
are needed for the interpretation of Milky Way observations. We also discuss in
some detail the formation of the Milky Way thick disk, chemodynamical models,
and the effects of radial migration.
