Kinematics and dynamics of the Galactic disc
  The Milky Way disc presents a warp, a flare, lopsidedness and other
deviations from a purely axisymmetrical double exponential density component,
both for the stellar and the gas component. Moreover, recent large-scale
extended kinematics maps of Gaia data have shown significant departures from
circularity in the mean orbits with radial Galactocentric velocities between
-20 and +20 km/s and vertical velocities between -10 and +10 km/s, asymmetries
northern/southern and other anomalies.
  The observed features are sensitive to internal and external forces,
especially at the largest Galactocentric distances. Here we review some of the
Galactic dynamics hypotheses that explain these anomalies: either in terms of
gravitational interaction, magnetic fields, accretion of intergalactic matter
or others. The gravitational interaction may be among the different components
of the Galaxy or between the Milky Way and another companion galaxy. The
accretion of intergalactic matter may be either into the halo, with a later
gravitational interaction between the misaligned halo and the disc, or directly
onto the disc.
  Most of the relevant observations are explained in terms of the accretion of
intergalactic matter onto a disc that is far from a simple stationary
configuration in rotational equilibrium. Other hypotheses only partially
explain some observations.
