A white dwarf in a binary system can collapse to a neutron star due to stable accretion from a non-degenerate companion or due to a merger with a white dwarf companion. In this talk, I will discuss the evolution of these systems prior to collapse. I will present simulations of accreting oxygen-neon WDs performed using the state-of-the-art MESA stellar evolution code. These include previously neglected effects such as Urca-process cooling and are able to reach length-scales that directly connect full-star simulations to past studies of the onset of the collapse process. I will also discuss work exploring the long-term outcome of the merger of two carbon-oxygen WDs. Beginning with simulations of the short-lived viscous disk initially present in these remnants and then following the subsequent thermal evolution with MESA, I will outline the interesting path that leads to their final fate.
