  The existence of neutron star mergers has been supported since the discovery
of the binary pulsar and the observation of its orbital energy loss, consistent
with General Relativity. They are considered nucleosynthesis sites of the rapid
neutron-capture process (r-process), which is responsible for creating
approximately half of all heavy elements beyond Fe and is the only source of
elements beyond Pb and Bi. Detailed nucleosynthesis calculations based on the
decompression of neutron star matter are consistent with solar r-process
abundances of heavy nuclei. Neutron star mergers have also been identified with
short-duration {\gamma}-ray bursts via their IR afterglow. The high neutron
densities in ejected matter permit a violent r-process, leading to fission
cycling of the heaviest nuclei in regions far from (nuclear) stability.
Uncertainties in several nuclear properties affect the abundance distributions.
The modeling of astrophysical events also depends on the hydrodynamic
treatment, the occurrence of a neutrino wind after the merger and before the
possible emergence of a black hole, and the properties of black hole accretion
disks. We discuss the effect of nuclear and modeling uncertainties and conclude
that binary compact mergers are probably a (or the) dominant site of the
production of r-process nuclei in our Galaxy.
