  With the first observation of a binary neutron star merger through
gravitational waves and light GW170817, compact binary mergers have now taken
the center stage in nuclear astrophysics. They are thought to be one of the
main astrophysical sites of production of r-process elements, and merger
observations have become a fundamental tool to constrain the properties of
matter. Here, we review our current understanding of the dynamics of neutron
star mergers, in general, and of GW170817 in particular. We discuss the
physical processes governing the inspiral, merger, and postmerger evolution,
and we highlight the connections between these processes, the dynamics, and the
multimessenger observables. Finally, we discuss open questions and issues in
the field and the need to address them through a combination of better
theoretical models and new observations.

High Energy Astrophysical Phenomena;General Relativity and Quantum Cosmology