  Due to the rapid longitudinal expansion of the quark-gluon plasma created in
relativistic heavy ion collisions, potentially large local rest frame
momentum-space anisotropies are generated. The magnitude of these
momentum-space anisotropies can be so large as to violate the central
assumption of canonical viscous hydrodynamical treatments which linearize
around an isotropic background. In order to better describe the early-time
dynamics of the quark gluon plasma, one can consider instead expanding around a
locally anisotropic background which results in a dynamical framework called
anisotropic hydrodynamics. In this proceedings contribution we review the basic
concepts of the anisotropic hydrodynamics framework presenting viewpoints from
both the phenomenological and microscopic points of view.
