The merging of two neutron stars is a true multimessenger event which includes gravitational waves, an electromagnetic signal and the emission of enormous numbers of neutrinos. In order to understand these signals we need a careful accounting of the microphysics that occurs during and after the merger. I will focus on the elements produced in these objects and the effect of two aspects of this microphysics; nuclear models/reactions and neutrino flavor transformation physics.  In particular, I will relate new developments in these areas to predictions of kilonova light curves and the astrophysical origin of the r-process.