  The differential event rate in Weakly Interacting Massive Particle (WIMP)
direct detection experiments depends on the local dark matter density and
velocity distribution. Accurate modelling of the local dark matter distribution
is therefore required to obtain reliable constraints on the WIMP particle
physics properties. Data analyses typically use a simple Standard Halo Model
which might not be a good approximation to the real Milky Way (MW) halo. We
review observational determinations of the local dark matter density, circular
speed and escape speed and also studies of the local dark matter distribution
in simulated MW-like galaxies. We discuss the effects of the uncertainties in
these quantities on the energy spectrum and its time and direction dependence.
Finally we conclude with an overview of various methods for handling these
astrophysical uncertainties.
