  The building of planetary systems is controlled by the gas and dust dynamics
of protoplanetary disks. While the gas is simultaneously accreted onto the
central star and dissipated away by winds, dust grains aggregate and collapse
to form planetesimals and eventually planets. This dust and gas dynamics
involves instabilities, turbulence and complex non-linear interactions which
ultimately control the observational appearance and the secular evolution of
these disks.
  This chapter is dedicated to the most recent developments in our
understanding of the dynamics of gaseous and dusty disks, covering hydrodynamic
and magnetohydrodynamic turbulence, gas-dust instabilities, dust clumping and
disk winds. We show how these physical processes have been tested from
observations and highlight standing questions that should be addressed in the
future.
