The observation of gravitational and electromagnetic waves from a binary neutron star merger in August 2017 conveyed key information on the nature of matter at supranuclear densities, on the origin of short-gamma ray burst, on the production site of of heavy elements via r-process nucleosynthesis, and on cosmography. Future multimessenger observations of this kind hold the promise to convey unprecedent insights on some of the most fundamental physics questions. A crucial and necessary ingredient to intepret these observations is the precise knowledge of the dynamics of the sources. I will talk about recent developments on the modeling of neutron star mergers using numerical simulations in general relativity. I will focus on the exploration of the the merger remnant and mass ejecta, and the dependence of the merger outcome on the binary parameters. I will discuss detailed models of the gravitational signal for the complete (inspiral-merger-postmerger) gravitational spectrum.